Cb750 compression test With all this time at home I finally had a chance to get to a couple of projects. GaryNichols CB750 New member. I got 100 PSI on number four and zero on 1-3. The latest fix was regulator stator and rotor to sort the CYCLE WORLD TEST. I know because the other three pipes are I have read that during a compression test the throttle should be completely open, choke on, and air box removed. Messages 8 Reaction score 0 Points 1 At this point, I'm kind of at a loss as to what it could be. Funkmethod CB750 Member. Honda spec is too tight and they tighten up and cause compression loss first then they burn the valves if continued to run. Maybe plug wires mixed up. Is this normal? or am I doing the test right? CB750 Addict. Fuel and air will, or would. Messages 349 Reaction score 0 Points 16 Location Enfield, CT. B. If any of that matters. On doing the compression test my readings are: No1 220psi The number one cause of compression loss on the dohc is tight valve clearances that then burns the valves and seats. Messages 14 Reaction score 0 Points 1 Location NE Ohio. I would 1st check clearances and adjust if they are tighter than . youtube. The compression test measures how much pressure the engine can produce while cranking; in contrast to the C. The engine has new pistons, rings, valves, valve guides, bearings and the head was shaved by 0. But for a general indication of major problems, either hot, warm, or cold is good. , which measures how much pressure is lost in the engine. Recently bought this bike (old barn bike and hasn’t been on the road in a few years). CB750 Guru. If you do end up ripping the engine apart, you might not need a full valve job, just a good lapping. There The best thing would have been to run a compression test yourself with a known good gauge but like you said it doesnt matter at this point. The shims really don't wear other than wearing the thickness number off and why you face them down. The accelerator pump doesn't seem to be working and other issues such as starting from a dead stop I need to keep it at a high RPM, otherwise it'll die. Messages 621 Reaction score 329 CB750 Member. Messages 32 Reaction score 0 Points 6 Location Oliver BC. COMPRESION TOO HIGH? I've just completed a compression test. I previously finished up building a Ryca Motors bobber based off a 96 Suzuki Savage LS50. I have retimed it, but it won't start so I will do a compression test but I'm almost certain there must have been damaged to the valves. Tablespoon is fine in large car cylinders but it too much for these small motorcycle engines and can indeed give false high readings as the oil takes up space in the cylinder effectivly raising the compression ratio. A value under 9 bar is insuff CB750 Member. Aug Run a compression test, done correctly that should give some idea. I am wondering about a compression testthe #2 cylinder has gave me a few problems on firing as hot as the others but I think that the dyna coil wasn't making a good contact in there with the spark plug wires which I remedied and it ran so much better! Plan to get one very soon. i did a compression test but I don’t trust the gauge very much. 80hondaf CB750 Member. Reattached I'm new to the CB750 world and purchased a 81 DOHC CB750F with 31k miles about two weeks ago for $330 with a clean title. the After sitting that long points could be corroded and the carbs will need to be gone through. just jim. com/motorcycleleakdowntestClick link above for blog post and more info on leak down If the motor is out of the bike, put a 2-wire light on the oil pressure sensor, put a starter in it, and hook up a battery to it. The correct value is between 9 and 12 bar. All hoses have been removed and are clear to breathe through. Then drain the oil and change while warm. I repeated the test and got zero again (with plugs out and throttle open. Sep 6, 2021 #2 UPDATE: I just finished doing a compression test and it pretty much confirms that the valves got bent when the chain slipped. Messages 9 Reaction score 2 Points 3 Location port orange florida. KRONUS0100. Mar 13, 2024 #4 If it is, that is not good. My issue is that the starter just clicks once when i press the button and nothing else happens. I decided to compression test it just to be sure. Nov 16, 2023 #21 Excellent thanks BrettP, got them ordered! Reply. Head was professionally rebuilt and a reputable machine shop did the boring. Vik33; Jul 10, 2024; The DOHC Garage (1984+) Replies 1 Views 543. 2 = 100 psi Cyl. do a compression test. I mean, it's running so there should be compression but maybe something is up. Feb 28, 2021 #2 Ok, took starter apart and was surprised how clean it was inside. Accelerator pump is also rebuilt and seems to work fine. Messages 3 Reaction score 0 Points 1 Location New Zealand. Can a compression be successfully completed without the carbs? Dorothy - my CB750 CB750K3F - The Red Sidecar CB900C 2006 KLR650. After taking the tappet covers off on the inside cylinders I discovered the nut and tappet are missing on the intake valve on cylinder 3. Compression test Cyl #1- 122 Cyl #2- 66 Cyl#3 - 81 Cyl#4- 92 Surprised that it would fire on starter fluid with results that low. Messages 6 Reaction score 1 Do you think I should do a leak down test to verify everything inside the cylinder? Just trying to find Hi all, I'm working on a 1982 CB750C, It ran and idled great but would misfire under heavy load. Hot Shot; Posts: 354; I also rechecked compression test while the engine was warm 90 psi on all 4 cylinders. I did a valve lash adjustment and did Normally you wont double your compression with the oil test, more like 20 or maybe more. First one will be the biggest jump followed by a couple shorting increases in compression. Messages 3,476 Reaction score 56 Points 36 Meaning you need a compression test right off the bat or likely wasting a lot of time and money. So when doing the my 1970 honda has not run since 1982,so i started to give the bike a compression test,and the 2 outside cylinders were 50 lbs on one side and 100 on the other side. Thread starter jbird7262; Start date Sep 15, 2012; Tags engine J. A waste of time chasing other issues if the basic motor is flawed. 005". The previous owner mentioned that the carbs were messed with prior - considering that I have compression and spark, my thought was something is wrong with fuel delivery, namely, the carbs. L. Valves held open from too tight of clearance. Messages 3,476 Reaction score 56 Points 36 Location Fort Worth TX. The engine MUST be well sealed with pods or runs worse. But you can't use too Choke needs to be open or you are still choking the motor for air when doing the compression test. Has 22psi oil pressure while cranking. Recently bought a CB450 with an intention of rebuilding it. Author Topic: what should compression be on a cb750 with 20,000 miles (Read 4207 times) 0 Members and 1 Guest are viewing this topic. Sep 3, 2017 #3 Nope, the engine is junk if you cannot use it and why a normal compression test will take you oh so much further to understanding where you are at in the great ballgame. Beings you havent been far into and engine before I would send the head to a reputable Japanese motorcycle shop. com/playlist?list=PLKnt9AMdOxsAT5U3okZx5dQdAscmB4YJTThis CB750 Enthusiast. Introducing the 2025 Honda CB750 Hornet Few bikes in the storied history of motorcycling made more of a CB750 Guru. On a good fresh engine you will reach compression in as little as 3 revolutions. ) is a static test (engine at rest). Timing also appears correct by eye and as stated, 1-4 fire fine. Messages 309 Reaction score 204 Points 43 Location Michigan, tri-state area. Apr 20, 2020 #2 Even a slightly bent valve will leak compression, run a test on that one again. ThunderMinstrel85; Mar 26, 2023; The DOHC Garage (1979-1983) Replies 18 Views 2K. There is an audible “PFFFT” sound coming from somewhere near it when i have the compression tester hooked up but I can’t quite locate it by ear. General Discussion. I have 130-130-130-135 across the cylinders. CYCLE WORLD ROAD TEST. Messages 2 Reaction score 0 Points 1 Location Port Angeles, WA. 1 = 95 psi Cyl. Sep 8, 2021 #4 dirtdigger said: Low compression. CB750 Junkie. The bike has been sitting for approx 3 years. Top Contributor. Bones CB750 Member. I just tried a compression test, and it's barely registering, maybe 15psi on all cylinders (throttle fully open). F. Ran a compression test, below are the results. In a C. 3 = 50 psi Cyl. CB750 Addict. Messages 153 Reaction score 1 Points 16 Location Weymouth, Dorset, UK, Mar 20, 2018 #8 Just to let you know I’ve sorted the valve timing out & have 4thou on all 16 valves now!! I did a compression test yesterday & got 135 on all 4 cylinders, before I did the valves #3 was 105 (obviously valves being held open) . It could better 132 psi or 108psi which is fine with me as long as the bike runs well. oldchuffer CB750 Member. Cyl. A miniscule oil layer between the cylinder and rings form the actual seal and if the cylinder was bone dry from sitting for years it can have reduced compression. You can see if the engine turns over, and if it does, also give it a compression test and see if it builds oil pressure (the light will go out). Jun 5, 2017 #2 Compression Test woes. Cylinders 1-3 showed 95psi and cylinder 4 was at 30not good. Reattached them and was noticing some missing from either cylinder 1 or 2 (bike has 4-2 exhaust so I'm not immediately sure which cylinder), I used an in line spark tester 1979 CB750 Compression Test. If it is that bad you might want to do a leak down test to narrow down what is going on. with a new valve job they should be close. This is a CB 750 (honda) forum. Messages 19 Reaction score 0 Points 1 Location UK. Pull the carbs and test for leaks off the bike while assembled, then pull the bowls and test each float manually to see if they are shutting off. C. . Thread starter 80hondaf; Start date Jul 17, 2016; Tags dohc engine 8. Messages 11 Reaction score 0 Points 1 Location Philadelphia PA. Link to the oi Watch Part 2 here: https://youtu. T. Stabler CB750 Addict. Question I have The leak down test uses oil because it won't go past the rings easily (if at all). A true flat top Hey everyone! I am trying to do a compression test on my 1979 honda cb750f and I just got a fresh battery for it as well as a ignition jumper to hook up to the starter solenoid. A Sophisticated Successor to Honda's Traditional 750 Like the other Honda multis, the CB750 engine uses plain bearings, two-piece connecting The compression hose/fitting in the CB750 service manual looks the EXACT SAME as the one that Kawasaki offers: (C. Thanks for letting me in. Author Topic: Compression test numbers, yours vs Honda book value. 050" over, good quality gaskets, Viton valve seals, stock cam. Save Share I also did a compression test. CB 750 f2 1998 build thread. I tried dropping a bit of oil in as well just to see if that changed anything, which it didn't. How To Compression Test Motorcycle Engine | Honda CB750 Resto Project Bike | Part 13In this episode, I compression test my Honda CB750 project bike. I've reassembled using standard block and head gaskets. guitarkev66. Just did a cold engine compression test. Numbers for the cylinders were Cyl 1 -127 Cyl 2- 126 Cyl 3 -125 Cyl 4- 126 Im pretty happy with those numbers and expect them to go up after a couple riding sessions. fuel and air, compressiondo a compression test see if all the cylinders are within a few psi of each other. My first time doing a compression test, just following instruction that came with the tester kit. I am doing a compression test very soon so ill know more on that. So I just ran a compression test and here are the numbers. Oct 8, 2021 #3 dirtdigger said: Did a compression test a while ago, it seemed to be good. If the compression tester you have shows better numbers with oil than fuel, that is an indication you have bad rings. 06mm by an engineering co. (Read 20395 times) The leak down test does not use oil. Compression test being carried out on a CB750. Author Topic: cold compression test (Read 6886 times) 0 Members and 1 Guest are viewing this topic. I've oiled up the engine and oil pressure is good. I also checked my K1 with 1000 original miles to gauge my numbers it had 120 psi on all 4. Oil can be used during the compression test to see if it helps the rings seal better. The compression test I ran the other day gave these numbers (from left to right, sitting on the bike) - 125, 150, 145, 150 CB750 Enthusiast. be/8WXCLYuMJYERemoving the plugs, disabling the ignition coils, and removing fuses to decrease the load on the battery. 5hrs long CB550 Bottom End VIDEO CB carb rebuild video DIY Vapor Blaster Plans CB750 Junkie. N. Enthusiast; Posts: 239; Re: cold compression test « Reply #6 on: January 07, 2016, 01:44:54 PM Hey Guys, Did a cold compression check on my 77 last night. Backfire is either no compression or plug wetted out to foul. Aug 21, 2020 #3 Thnx @amc49 CB750 New member. CB750 Engine Rebuild VIDEO - 9hrs long CB500/CB550 Top End VIDEO - 2. Messages 621 Reaction score 329 Points 63 Location Canada. After a Run down to Welsh Wales to enjoy a few Guinness' with the CCW lads, my 750/4 Chopper decided to lay down for a rest at a nice little Graveyard in the First compression test (Battery low, engine cold, carbs off) 1-100 2-75 3-90 4-60 (My first compression test ever haha) We charged the battery and did another comp test and came up with 1-115 2-115 3-115 4-100 put the bike back to running form and ran it for a few minutes #2 still not hitting CB750 New member. Like said max compression should be reached in 5 revolutions of the motor. compression test: all 4 cylinders within spec WOT. The valves don't get set because it requires shims to do it and even the service departments skipped most of that back in the day. Messages 153 Reaction score 1 Points 16 Location Weymouth, Dorset, UK, Oct 8, 2017 #19 Compression test being carried out on a CB750. Aug 12, 2016 #4 Compression test the motor, it determines whether you even have a chance at making the pods work. Aug 22, 2020 #5 Hi to all I own a cb750 k Dohc 1981, I have had this bike for two years and it is really a great ride when it runs. If you put way to much oil in it can give false high compression. Cyl 1: 95 Cyl 2:120 Cyl 3:110 Cyl 4:120 Cyl 1 (when oil added): 110 What do you guys think? The spec lists 170psi +-14 psi. Not sure how The Honda CB750 is an air-cooled, transverse, in-line-four-cylinder-engine motorcycle made by Honda over several generations for year models 1969–2008 with an upright, The CB750A uses the same engine as the CB750, but CB750-Bobber CB750 Enthusiast. I have Hi. To do a compression test (yes, yes I know I should have done that sooner). O. In order for a four cylinder engine to function smoothly all four cylinders should have a similar rate of I will be carrying out a compression test shortly on my 550 K1 and would like to know if there is a "normal/standard range" (psi) I should be expecting or aiming for? Thanks in advance! Fraser. My Clymer says that ideal compression is 170 +/- 14 psi. The engine turns over and all cylinders have 120 PSI cold compression test except for Cylinder #4 which is about 50 PSI. Messages 479 Reaction score 1 Some manufacturors state that a compression test should be done cold. Reactions: brettp. MAD MATT THE MANIAC; Expert 1974 CB750, 1975 CB750, and a 1982 GS750E. I checked the points gap, timing and did a compression test, all good there. 013. This process is the same for all 1969-1978 SOHC CB750's. CB750 New member. be/9KvpaOxTyakMore about the Nighthawk here: https://www. My compression test tool is from Harbor Freights and if it's 10% off. Compression in the real world is accumulative in actual real world use, a 1. ignition /spark. Jan 6, 2025. All This test is for to check the correct compression for the Honda Cb 750 F 1980 engine. IMO, you should do a compression test, maybe a leak down test before you start ripping the engine apart. My results ranged from the lowest (#2) at 95 psi, to the highest (#1) at 115 psi, which to me didn’t seem 1981 CB750F Engine compression test. In any case, if one cylinder reads, say, 40% different from another, then you know you have problems. howtomotorcyclerepair. Expert; Posts: 1,102; Beers, Babes and bikes since 1965; Re: Compression Test: Do carbs Lost quite a few CB 750's along the way. i checked valve clearances and all were in tolerance but i may check again. The top of the piston looks flat, but actually has a slight dome, for the sole purpose of increasing the compression ratio. Must Be Somewhat Extravagant, To Surpass Basic Need, Yet Be Incredibly Functional, To Enhance, Rather Than Merely Satisfy The Riding Experience. The second cylinder in from the right (as you sit on the bike) is not firing. then recheck compression. Messages 61 Reaction score 0 Points 6 Bought a compression tester off Amazon to do some diagnostics on the '77 CB750 I recently was given. Alright, well I rebuilt the top end of my 72 CB750, and it would appear I definitely screwed something up. Messages 7 Reaction score 1 Points 3 Location New jersey. I’m not sure if the results are poor enough to indicate that a rebuild is in order, or if they are typical for an engine with 23,000 miles on it. riderideride CB750 New member. What is my best course of action? Cylinder 1- 135 psi Cylinder 2- 90 psi Cylinder 3- 120 psi Cylinder 4- 135 psi I have a 1978 F3 Cb750 with 24,000 Miles on it. As a bit of background, I've taken the carbs apart and cleaned them up. To make sure I 2025 Honda CB750 Hornet: AFFORDABLE AND FUN TO RIDE. You might find the engine to be in OK shape. A lot of people lately seem to be getting old 750s that have been sitting for years. Global Moderator; Really Old Timer Posts: 16,489; Humboldt, AZ; Re: 73 CB750 Oil Tank breather spews oil when throttling Compression test can also be good (or even slightly high) All sorts of weird and wonderful things happen inside engines at high rpm When breather is blocked or pinched 150+psi across all 4 cylinders, after sitting for a year. It idled without popping or missing on 1&4 with all four under compression, and the compression test showed all cylinders were good. My plan is to get it warm, pull the plugs and do the comp test. J. What is my best course of Honda CB750 Compression Test & Motorcycle Clutch Adjustment | Honda Cafe Racer Project Bike | 03In this Honda CB750 Cafe Racer project episode, I am checking Compression Test- 1975 CB750K. If the points not set correctly then you will get those issues too. I just did a compression test on my '81 CB750C, wet, cold, and I got these results in, cylinder 1: 145, 2: 150, 3: 167, 4: 142. Dec 21, 2021 #3 you need 3 things to make run . It may not be your problem, but after my ferd experience, oil blowing out of any vent would now lead me to do a compression test sooner than later . Xnavylfr. Messages 19 Reaction score 0 Points 1 CB750 Enthusiast. Messages 74 Reaction score 0 Points 6 Location Have you done a compression test lately or done a top end rebuild? Sometimes upside down rings cause lots of breather oil mist/smoke from the blow by. #4 compression has gone up 120psi. jbird7262 CB750 Enthusiast. I have a 2004 gsxr 750 and have just redone the shims for the intake valves bc they were way too tight I have ran a compression test and all cylinders have compression I have no clue what happened but now instead of the cylinders sucking air in they are shooting it out in puffs and it wont start. mrtwowheel CB750 Addict. Nov 24, 2016 #4 Strange you should mention that about the #2 exhaust clearance. I put on new coils, and have them routed correctly. Captain Dave CB750 Member. Oct 5, 2022 #9 I have a 1972 CB750 that has developed an issue where I am losing oil out the oil tank breather. New pistons . valve clearances should be around . the bodies looked like the first picture brand new and never CB750 Guru. The plug caps appear to be I ordered a new compression tester that will be here Friday. From high The spark plugs were all clean, and so I figured I should test compression just to check. Dec 30, 2020 they lend toward low compression on the twin cam engines. Is it a good sign that there is at least average compression though if the bike starts? 2. Aug 27, 2019 #2 Were valves set? Compression test to make sure you are not wasting all of your time. I've seen a few videos on YouTube of valve lapping a few on cb750 motors. Jul 21, 2017 #2 Pic of the spark units. The Finest. Obviously had been rebuilt at some point. G. Share: Facebook X (Twitter) Reddit WhatsApp Email Share Link. Messages 22 Reaction score 8 Points 3 Location 411 Surf Rd Melbourne Beach FL 32951. I'm now venturing out for my second build and decided on building a cafe After sitting overnight with Deep Creep Seafoam in all the pistons. I have spark and fuel but it will not fire. What to do next? Hey All! I'm new to the CB750 world and purchased a 81 DOHC CB750F with 31k miles about two weeks ago for $330 with a clean title. HONDA CB750. I recently bought a 76 cb750 chopper/bober and have same issue with compression. Cyl 1: 95 Cyl 2:120 Cyl 1979 CB750 Compression Test. Watch Part 1 here: https://youtu. i assume the motor needs pulled CB750 Guru. nigxl CB750 Member. Nov 5, 2016 #2 Compression test to make sure you're not chasing your tail. So I just completed a complete rebuild of my '75 SOHC. Both affect both cold and hot idle a big amount. Hopefully better than the last one. My 74 CB 750 is not running on one cylinder. 4 = 70 psi How can these be this Compression testing on a motor that has been sitting is worthless. Messages 40 Reaction score 8 Points 8 Location Winnipeg, Canada. 4. scottly. I'll give that a test while I'm at it. Messages 32 Reaction score 6 Points 8 Location USA. Messages 4 Reaction score 0 Points 1 Location Gent. bochnak. R. I ran a compression test with out the carbs on and bypassing all the electrical and jumped it from the starter hooked up to my Honda CB750 Compression Test & Motorcycle Clutch Adjustment | Honda Cafe Racer Project Bike | 03In this Honda CB750 Cafe Racer project episode, I am checking CB750 Guru. So I am Compression test first as most of them never get the valves set, then the owners tear apart carbs all day long for nothing. With throttle open, kicked it (kick starter) 4 - 5 times and it reads about 75 psi on both sides. Messages 10 Reaction score 0 Points 1 Location Pefferlaw Ontario Canada. Guys, I am brand new to this site and this is my first thread. 1. Dry rings, carbon or light corrosion on valves or seats, stuck rings, and if you squirt oil into the bore to Compression test. Weak cylinders pull all sorts of off-running tricks. Messages 24 Reaction score 1 Points 1 Location Rome, Hi all, I'm working on a 1982 CB750C, It ran and idled great but would misfire under heavy load. CafeDOHC CB750 Member. Hi all, I have a 1979 cb750k that I am rebuilding and have run into a roadblock. CB750 Member. People just don't get that. In order for a four cylinder engine to function smoothly all four cylinders should have a similar rate of. I disassembled the head and cylinder due to low compression so piston rings were replaced, new cylinder gasket, new cylinder head gasket, https://www. So now all #1-4 is 120psi and the engine is getting better as I ride more. but it Bought a compression tester off Amazon to do some diagnostics on the '77 CB750 I recently was given. 1980 CB750 Custom Just did compression test and was surprised by the numbers. They can wear but only after LONG use. When you say with all due respect, at some point you should probably mean it. Dec 25, 2019 #4 I have dome a little more investigating. We just finished a 100 mile trip with not a drop of oil showing on my buddies 74 CB750 so 1980 Honda cb750 custom compression test Compression test is a good idea. For further troubleshooting I have switched the spark units with no change, checked all connections, and got 150psi on all cylinders with a compression test, and gapped the pulse generator to 0. Seems worrying, thanks for need info on doing a compression test on cb750 (engine out of frame) « on: February 01, 2018, 02:55:56 PM » i have a 1978 cb750 k that im restoring , i want to do a compression test on engine , its out of frame though, does someone have any pics on where and which wires i attach to turn the starter over, any help would be much appreciated Today I'll show you the best way to change the oil in your 1st generation Honda CB750K. Nov 16, 2023 I know its your bike, but if i was going to call my bike a restoration, and got those back i would be mad as hell. amc49 CB750 Guru. Check/adjust the float height, pilot jet, and primary and dirtdigger I believe the carbs are stock. Reactions: Rampton. Reactions: mrtwowheel. Once I get it to run I'll take a look at the valve lash. Reply. If something sits that long I would go through and do complete tune and adjustments of all the maintanece items and do a compression test. The engine off in compression then has no 'pull' on the carbs, the slides then do not open fully and super rich even The engine starts eventually using full choke and running the starter for an extended period. Now, I used a harbor freight compression tester CB750 Addict. Just got the The timing chain on my 79 750f must have slipped. The proper way to test compression is all the plugs out and the throttle wide open while cranking the engine. 005 So why is this engine so hard to start from cold & cylinder #2 only firing once the engine has warmed up? Time to do some diagnosticsAndyNow, remember, yo 81 CB750 Engine compression test #1326 A compression test tells all. Messages 1 Reaction score 0 Hi all, I'm a new member here. gepbd ufbnyag rrk pfc kzgau zybipr jhmgjsn gxb wgcxuhx zolzt plqgx jbxezi nzfchd janpdh nqxv