QuestionQUESTION: Jan, I just stumbled on this thread and you appear more knowledgeable than other "experts" whose opionions I've read.
In any case, I've got a 79 CBX carburetor rack in for restoration. (Check me out on ebay usename oldschoolcarbs.)
When I removed the bowls it was obvious that the float heights were set to run extremely lean, which I took as a sign that a previous mechanic did a poor job and perhaps explained why it sat for 15 years. Upon further disassembly I found 2mm thick phenolic-core washers raising the needles. That seemed excessive beyond anything I've heard of for raising slide needles so I called my customer.
He reports that the carbs were once worked on by a Honda certified carburetor expert. He had no idea specifically what that individual had done other than that it ran very well before it went out of service.
I'm curious to know if our "expert" knew something the rest of us don't know or it he simply couldn't get the floats right and took an easy way out.
I'm returning the carbs to factory spec unless you have information on this particular mod that makes it preferable.
Nothing else is modified and all inside parts are Keihin branded and are all original spec.
THANKS MUCH!
Jack
ANSWER: Hi Jack, Thanks for your question. I have seen your ads and am glad you asked me this. While there can be reasons to deviate from stock, usually the performance is changed somewhere else adversely. If the needles are raised (enrich mixture) but floats are dropped (weaken mixture) for a given air velocity, I wonder what the overall changes would be at the different velocities... I would imagine that since the total needle lift range is the same, the needle goes slightly higher but at that position the difference will be marginal, so the carbs will be leaner at the top end, which may give a leaner setting and give more performance, as the WOT settings from the factory are typically slightly too rich to stop engine damage.
I cannot believe an expert couldn't get the floats right since they're so easy to do. I wonder if the jets had been drilled, since that was common back then. The numbers would still be stock, but the jets would be a different size?
It may be worth noting any deviations from stock, also it would be key to note any airbox modifications and exhaust changes which the owner can answer easily, secondly any valve work or camshaft would would be interesting addtional information. We are racing a CBX occasionally so this information would always be useful. please feel free to contact me direct at mrcbxatatt.net
Conversely if the rest of the bike is stock, all the carbs changed back to stock should not hurt anything; the owner's feedback should tell you if things are different.
Are you in the ICOA?
Hope this helps,
Sincerely, Jan
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QUESTION: Jan, don't get me started on "experts". I've got a set in the shop that was done in the last thousand miles by someone whose name you'd recognize. He couldn't get the floats right either. Problem was that he installed aftermarket seats that aren't milled properly so the needle sits so high that with the tangs bent as far as possible it's still VERY lean. Switching to keihin needles and seats solved the problem. Most puzzling is that the rebuilder claimed that he put 150 miles on the bike before handing it over just to be sure everything was dialed in. NOT.
We're all entitled to screw-up once in a while but this one is over the top. All my poor customer wants is to feel safe getting more than five miles away from home without fear that it'll begin stalling out and failing to restart.
In any case, the carbs in question (which are not the ones from my little tirade) are going back to all spec.
Per your comment about jets, they all probe to proper size and the passage plugs are tight.
All in all I'm thinking that the current expert belongs in the same category as the other.
FYI, no I don't belong to any clubs as yet. My name, however, did come up on one of the boards. Someone questions my...ability, which is entirely natural seeing as how I'm an upstart. I'd grouse too, but hey, you gotta eat a few whilst getting your name established in a competetive niche.
Thanks again for your input!
Jack
PS: Have you ever used a digital O2 sensor to see what's going on at all ranges on the CBX? I'd be curious. Readings for my all-stock 1984 VF1000 show a respectably even mix all the way to rev limit. All I've done in the way of mods is nix the CA emissions control system. I've got a mule CBX engine but no whole bike and nobody around with one to let me test.
AnswerOh yes lots of experts out there but only a few who really know what they're doing. Lots of interest in aftermarket seats and needle valves because of price, however not getting the OEM's is more expensive in the end!
We raced a cbx a couple of years ago, but we want to get the carburation right and will need to find a dyno with lambda sensor to check the performance through the rev range...
If you can do carbs well at the price you advertise, you will not go short on work!
Jan
