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1980 cb750 won't rev

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Wannabecummins

1980 cb750 won't rev

Hey guys,

So I posted a few pictures of my bike. Got it running last summer, it had been sitting for 13 years. Rode it all last summer. This spring I took the bike in to get the carbs cleaned and a tune up done. When I got the bike back I took it out for a ride. It falls flat on it's face at 4200-5000 rpm. Sometimes it will rev a bit more or a bit less. Took it back too the shop and they thought the jetting was off. They re-jetted it but the problem is still there. Bike runs like a raped ape up too 4200. I'm currently at a loss. Any input would be appreciated.

Thanks,
Brad

TOOLS1

Re: 1980 cb750 won't rev

Administrator

Did you change the air filter, or put pods on it?
TOOLS

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1976 CB 750-A X 2
1977 CB 750-A X 4
1977 CB 750-K
1976 CB 750 F
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1973 CB 350
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Re-run

Re: 1980 cb750 won't rev

Administrator

Well, if the pics are an indication, looks like the airbox is still on it. So I suppose then it might be what type of filter is in it.

Does the rpm pick back up after that range, or does it stay there and sputter? I would do a plug chop at that range and see what the plugs look like.

The ride IS the adventure. The destination is just to get gas!

Wannabecummins

Re: 1980 cb750 won't rev

In reply to this post by Wannabecummins

It just stays there and sputters. I've changed the plugs since it came back from the shop. They all looked good. I actually haven't checked the air filter. Last time I looked at it, it was clean.

Re-run

Re: 1980 cb750 won't rev

Administrator

What color are they? It really sounds like some sort of fuel issue. You plugs should say if it is rich or lean.

They should be a light tan. Try this, when you hit that rpm, try pulling the choke a bit and see if the sputter is worse or if it gets better. Obviously you know which way to go depending on what happens.

The ride IS the adventure. The destination is just to get gas!

motogrady

Re: 1980 cb750 won't rev

Administrator

sounds like the shop screwed the carbs up, my vote is clogged fuel passages in
carb on backside of jets.

Re-run

Re: 1980 cb750 won't rev

Administrator

I kinda think so too, thats why I wonder the plug color. it should indicate a fuel issue.

I suppose it could be electrical.

The ride IS the adventure. The destination is just to get gas!

Wannabecummins

Re: 1980 cb750 won't rev

I've played with the choke while it's doing it. Doesn't make any difference. I tested the cdi's and had one bad one. Replaced them and didn't change nothing. It's been awhile since I pulled the plugs out. I'll yank them out and get back to you guys.