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CB750 Barn find project - First Timer
Underdog1:
Aha progress!
had the carbs off again, blew all the airways with a compressor and plenty of carb cleaner, reassembled and i think i had the float valves in upside down! although i did reassemble how it was when i took it apart. Cheers previous owner.
Chucked the carbs back on the bike and used a hairdryer this time to soften up the rubbers which made it 100x easier. Tried to kick her over and didn't get anything, checked the battery and it was like 7v. Got a good battery to jump it off and still couldn't get her going and by this point i imagine i had flooded the plugs so i took the choke off and kicked her with a wide open throttle and she sprang into life!!
http://sendvid.com/mw9r6td9 - Vid of her running
Now she wouldn't idle but thats probably due to the carbs not being set up correctly and not having an airbox on but she ran as long as i kept her at about 2000rpm.
Not all good news as cylinder 2 didn't seem to be firing right as the downpipe was only slightly warm compared to the others being too hot to touch, and after i switched her off i could hear a hissing and drips of oil coming from the left hand engine cover.
What do you think the issue could be? I plan on pulling the engine apart but its good if i can't perhaps pre-empt possibilities by doing some research :)
Overall a definite step in the right direction!
MarkCR750:
Great news, put the air box on and it will tickover , makes a huge difference with it off, No2 is either not getting a spark or fuel, check the HT cap is firmly screwed to the HT lead first, if that doesn't work, swap the cap with one of the other caps, by actually unscrewing the caps and swapping them over, don't swap the leads,and see if the problem follows the cap, if that doesn't work check the plug is getting wet with fuel if it isn't you might have a blockage in the carb, but before anything else try with the airbox fitted, try holding revs at 5k and see if the pipe gets hot, if it does your primary jet is blocked on that carb, holding higher revs means it's running on the main jet, regarding the hissing god knows, is the breather in the top of the cylinder head clear?, pull the pipe off for now.
PS video link doesn't work, YouTube is more reliable.
Underdog1:
--- Quote from: MarkCR750 on August 04, 2016, 06:36:04 PM ---Great news, put the air box on and it will tickover , makes a huge difference with it off, No2 is either not getting a spark or fuel, check the HT cap is firmly screwed to the HT lead first, if that doesn't work, swap the cap with one of the other caps, by actually unscrewing the caps and swapping them over, don't swap the leads,and see if the problem follows the cap, if that doesn't work check the plug is getting wet with fuel if it isn't you might have a blockage in the carb, but before anything else try with the airbox fitted, try holding revs at 5k and see if the pipe gets hot, if it does your primary jet is blocked on that carb, holding higher revs means it's running on the main jet, regarding the hissing god knows, is the breather in the top of the cylinder head clear?, pull the pipe off for now.
PS video link doesn't work, YouTube is more reliable.
--- End quote ---
Good call on the breather, took a fair amount of compressed air through it until it finally spat a glob of something out. The hissing ceased after this. Couldn't actually get the airbox on! It didn't come fitted to the bike and it's like the plastic boots are too small to fit on the carbs, maybe it's just the ancient plastic. In going to go down the pod route (cue eye rolls) so not too fussed anyway. Checked the HT lead for cyl 2 and got a faint click when I pressed down hard on it and the cyclinder seemed to fire properly after that so I think it's just a dodgy cap.
Going to pull the engine out when I get a chance as I'm getting the frame powder coated, even though I'm inexperienced I'm up for opening the lump up and refreshing whatever needs doing to keep the old girl running for another 40 years. What are the typical things that need addressing?
Finally I did notice that the final drive spindle for the front sprocket was spinning when revving the bike in neutral - is this just due to there being no sprocket or chain attached or is it some sort of fault?
Cheers!
MarkCR750:
If you are going to use pods you'll need bigger main jets, I've used 135's in mine with a 4 into 1 exhaust and the mixture was bang on when dynoed, also check out my thread "how to make pod filters work", (no roll eyes on this forum , it's a league of gentlemen!), spindle spinning in neutral is normal, regarding what's typical when stripping the engine?, it's totally down to the engines previous life, have a search around the threads on this forum and you'll get an idea of the problems you might face, but you'll probably enter a world of pain, most do , I've rebuilt various engines over the years but when the time comes to rebuild mine I'm giving it to Trigger and paying for his expertise, the cost will be more than offset by me being able to spend my time out riding my other bikes and knowing the jobs been done perfectly (Trig you can knock a fiver off my bill for that 😄).
Underdog1:
--- Quote from: MarkCR750 on August 04, 2016, 10:32:02 PM ---If you are going to use pods you'll need bigger main jets, I've used 135's in mine with a 4 into 1 exhaust and the mixture was bang on when dynoed, also check out my thread "how to make pod filters work", (no roll eyes on this forum , it's a league of gentlemen!), spindle spinning in neutral is normal, regarding what's typical when stripping the engine?, it's totally down to the engines previous life, have a search around the threads on this forum and you'll get an idea of the problems you might face, but you'll probably enter a world of pain, most do , I've rebuilt various engines over the years but when the time comes to rebuild mine I'm giving it to Trigger and paying for his expertise, the cost will be more than offset by me being able to spend my time out riding my other bikes and knowing the jobs been done perfectly (Trig you can knock a fiver off my bill for that 😄).
--- End quote ---
Cool I'll check that thread out, I'm also looking at a 4 into 1 so hopefully 135s will be in the right ballpark for me too.
Im expecting to have to get my hands dirty with the engine and could easily get someone else on the job for me but as I've never done this before I feel like if I don't do it now I'll never be able to. I'm off to the states for 11 weeks on the 25th with work so will have to put things on hold soon, and in not sure if I want the engine in bits for that long as when I come back ill probably never work out how it goes back together again ahah. On the flip side there's lots of cool bike shops where I'm going and my return luggage allowance is 50kg!
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