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My '75 Honda 750 runs perfect For about 20 min... FIXED! :)

1014 Views 4 Replies 4 Participants Last post by  mitchellsk
My '75 Honda 750 runs perfect For about 20 minutes and then starts running less than perfect, missing on at least one cylinder, but still drivable. If I let it cool off for 30 minutes or so it runs perfect again for about 20 minutes then the same missing again on some cylinders.

I've just completely torn down the carbs for complete cleaning over that last week, rebuilt them, and put them back on and still the same issue.

I just installed all brand new plugs, one heat range cooler, gapped at 26 thou, and still the same issue.

It has fresh premium grade fuel for the last couple tanks, with a bit of Lucas fuel treatment, and still the same issue.

'75 Honda 750, Stock engine, stock jets, 4-2 exhaust.

Again, if I let it sit for 30 minutes or so after acting up, it runs perfect for about 20 minutes then starts missing so I'm thinking something is getting up to operating temp and then unhappy :(

OR could it be taking that long to get fuel starved and then resting for a few minutes lets the bowls fill back up??? (hmmm) Again, this is happening before AND after the carb cleaning/adjustment. This is happening while driving stop-and-go around the neighborhood with stop lights, signs, etc... so it's not high rpm driving.

Ideas please?
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Re: My '75 Honda 750 runs perfect For about 20 min.... FIXED! :)

Thanks for the ideas all.

Immediately after I had the fuel starvation idea I took it for another drive. It was actually probably only 5 minutes and not 20, my bad.

After it started acting up I stopped at a gas station cause I couldnt think of another reason to let it rest for a couple minutes. I took my time to put a couple dollars in the tank, maybe 5 minutes. Drove it and it ran perfect, so I figured it wasn't heat related, for another 5 minutes and it started acting up again.

Before I got back to my driveway I cut the fuel supply off and then when I got to my driveway I shut it off and coasted in.

Pulled the bowls off and #3 was quite low with maybe only about a 1/4" of fuel in the bowl so I adjusted the float level a hair and drove it for 90 minutes in town and on the interstate (higher sustained rpm) with no problems!!!

#3 was being fuel starved with the float off just enough to get it going but not enough to keep up with demand.


Thanks again for the suggestions, I was thinking coils too at first.

I think I'll actually drive it to work tomorrow!
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