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Post by KevinH on Sept 17, 2013 18:35:11 GMT -4
1975 CB750F I've had for a little over a year had recently developed a bad habit of "jumping." What I mean is that when I am accelerating or have any kind of twist on the throttle it sputters like it is about to die. But the thing is, it never does and when I idle it is fine. Also when I am in neutral and accelerate there are no problems.
When I checked my float bowls and drained the gas into a bottle there was a substance on the bottom that was almost orange or pink? For curious parties I have a photo but cannot post to the board as I am on my phone. I'm trying to get this fixed ASAP as I want to enjoy the fall weather as much as possible. If someone is willing to come help that would be the best, my number is 614 371 22 six one. Text or call.
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Post by KevinH on Sept 17, 2013 19:03:55 GMT -4
It could be a timing issue or a carb sync problem. Or a lot of things. Or the pin holes I filled with bondo are getting eaten away by the gasoline. Another set of eyes would be appreciated.
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Deleted
Deleted Member
Posts: 0
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Post by Deleted on Sept 17, 2013 19:53:59 GMT -4
do you have in-line fuel filters installed? if not, I recommend a clear type (Briggs at Tractor supply) so you can see the crap that is no doubt coming from the tank and settling in the main jets and everywhere else.... causing the problems. if your petcock has a pre-screen, it'll be clogged too, slowing fuel supply under accel.
next - check for vacuum leaks, dry/cracked/air leaky carb boots. spray some carb cleaner on the boots while at idle. if the idle increases, you have air leaks, also causing problems. make sure your carb sync nipple covers are there and not dry rotted.
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Post by KevinH on Sept 17, 2013 20:24:04 GMT -4
All those things seem to be there. I have an inline and it isn't catching anything. My carb boots are still pliable and not cracked. Carbs are in great shape. If it helps to confuse the problem, it first occurred during a 3 hour ride causing me to head home ASAP.
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gr1976
Learners Permit
Posts: 351
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Post by gr1976 on Sept 18, 2013 8:34:16 GMT -4
Try running with the choke on (or in a few different positions) if it gets better there's something in the carbs
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Post by tango911 on Sept 18, 2013 23:09:16 GMT -4
Hit me up if you cant figure it out Ive been running a part time shop out of my home. CB750's are my thing.
steve
317-85zero-63five4
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Post by novafrk on Sept 19, 2013 10:31:20 GMT -4
What do the plugs look like? It sounds lean from your description. Are you running stock air filter and exhaust? If you are running pods and / or low flow / no mufflers that will cause it to run lean.
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Post by KevinH on Sept 20, 2013 10:33:40 GMT -4
Hey all I figure I should put together a better description of the problem.
When I start the bike it idles at 900 and sounds great. I let it warm up a bit then I take it around the corner. Everything feels fine. I get about half a mile out and the bike starts to kick on lower RPMs. It makes taking turns a nightmare but so far the bike hasn't died. This all started after a 3 hour trip and thankfully it was at the end when I could get it to the garage.
What I have done so far:
I pulled the airbox and the carbs and went through both. There wasn't a problem in either. (everything on the bike is stock except the handlebars and the turn signals.
I adjusted my air/fuel mixture to be a 1 full turn, 3/4 of a turn, and a turn and a half. This hasn't affected the problem.
I pulled my sparkplugs (well 3 of them, the one in cylinder 2 is giving me trouble with getting my socket the right angle to get it out) they were matte black and cylinder 4 had a little bit of white residue.
I synced my carbs using a vacuum gauge and everything was fine except when I accelerated to around 3 or 4k with my idle adjustment screw the bike wouldn't stay stable at the RPM.
I used the method mentioned above to look for a leak and there was no change in RPM when I sprayed both the boots from airbox to carb and carb to engine.
Compression is right at 170 for each cylinder.
There was a little bit of gas found on the airbox boots.
In my floatbowls was a bit of residue that didn't look like water that has since gone away.
I checked my timing and it seems to be a bit off (I can't rotate the plate far enough counter-clockwise to reach the F) and I bought an electric ignition from PAMCO so I have been waiting to put that on to fully correct that problem.
I have gone through the wiring harness and there isn't a short of any kid. I hope this helps as I am trying to participate in the Gentleman's Ride next weekend. I will be giving Tango a call and hopefully we can get it sorted out but any advice is appreciated.
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Post by tango911 on Sept 21, 2013 5:54:16 GMT -4
im off on tue and wed all day.
steve
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