Hello, one and all.
I’m in the middle of winter maintenance on my CR 80 shifter. I’m planning on swapping out the stock round-slide carb for a flat slide. However, I’ve got a fuel issue. Coming out of corners, etc. the engine bogs due to lack of consistent fuel delivery. Currently running a single mikuni-style square pump. Is there a fix(s) for this without going to a pump around system? Open to any and all suggestions. Thanks a lot,
Can you describe what you mean by bog and which type of turns? There’s a couple types of bogs:
1. motor falls completely flat and feels like it’s sucking air. No power at all. This is usually a severe lean situation at some point in the carb (fuel delivery, pilot, needle, main).
2. motor has some power but is very sluggish (not crisp when getting on throttle). Usually too fat.
I run a cr125 with a pump-around, so I may not be the best to advise you. However, most of the people I’ve known who run a stock carb/pump setup don’t have significant fuel issues coming out of turns. They may hickup or fall-flat in longer turns, but are OK otherwise.
Have you tried different pilot jets? You may be too rich or lean on the bottom end of the jetting? I know you can’t try anything for a while, so you may want to try different jetting setups instead of a pump-around.
Oh yeah…. has the pump been rebuilt and in good order? That’s often a culprit.
One more type of bog, but probably not the case. Many drivers tend to use too much of the lower power band and the motor bogs when it’s too low in the rpm range. In other words, it’s not ‘on-the-pipe’ when they get on the power. Anyway, if you think you’re too low on the rpm’s, try a lower gearing (or shift down one more) to keep it rev’d up.
I assume you are currently running the stock Keihin carb.
Have you purchased a flat side carb yet?
Make sure you get a Mikuni TM28ss carb, from a Suzuki RM80, this is what works the best on CR80’s.
Don’t know what altitude or what air filter configuration you are running. I run a K&N style filter at about 1,000 ft above sea level, running 37.5 pilot jet, 195 main jet. This should get you in the ballpark as far as jetting goes.
CR80’s do not like to be rich, if they are too rich, when backing off the throttle after a long straight it will bog when you hit the gas coming out of corners.
Hope this helps
#55 Honda CR80
Based on experiencing a very similar sounding problem on a 125 shifter, check your fuel pickup in the tank. If the hose on the pickup has become stiff with age, this will cause fuel starvation in or coming out of corners, as the pickup cannot adequately follow the sloshing fuel. Additionally, I have found that the square dellorto pumps perform far more reliably than any of the mikunis. Others may disagree, but since changing to the dellorto pump, I went from a mess with it every race scenario to a much more pleasant mess with it never situation.
Thanks one and all for the very helpful responses!
My fuel line situation is in good working order.
I’ll look in to a dellorto square pump.
Thanks for the specific make/model of carb recommendation for the CR 80. I am currently running the stock Keihin carb.
I’m betting it has a lot to do with jetting; the motor felt like it was signing off halfway through the powerband in some turns and straights; and a plug test showed it was on the rich side. ( motor has excellent compression )
I wanted to swap to a flatslide carb due to my experience with them in MX and sleds. I’ll keep adjusting the jetting and hunt for the Mikuni model.
I especially appreciate the jetting suggestions. I realize they vary based on many conditions, but a starting point is very helpful. All comments and suggestions welcome.
Thanks very much!
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