My Old Carb Issues - Revisited

[wonderboy]

I have a theory and a possible solution to my past carb issue, and want to run it by the group to see if anyone has either thought the same thing, or even tried the same solution.

First, my problem. In the process of restoring my old 200ES Big Red, I went completely through the carb because it just wouldn't run right. I kept fighting it, and eventually had replaced every jet, needle, holder, etc that was available from Honda. Yes, I used all original Honda carb parts, and this thing still wouldn't run. The symptoms were a very erratic idle. It would have a very lazy return to idle, it would hang, and was just very difficult to get to idle at a consistent RPM.

Eventually, I gave up and bought an E-bay carb, bolted it on and away I went. The e-bay carb, while a huge improvement over what I had (and still is very usable) just wasn't like the OEM carb when it was running good.

So on to my theory and solution. Is the basic problem with these old carb that just don't want to run right the the slide is just too worn? The way I figure it is that the more the slide wears, the more air can leak around the sides of it (not huge amounts of course, but I don't think it takes much). I think it is these subtle air leaks around the sides of the slide that is allowing erratic amounts of extra air through the carb, and thus the return to idle problems and erratic running at idle.

So for a solution, how about sending the slide out to one of these places the coats pistons with anti friction coatings? I've read about them and they seem like they'd stand up to the task on a carb slide, and they add roughly a thousanth (0.001"). I'm going to take some measurement of the bore and slide and see what the clearances look like. So my theory hasn't gone much farther than just thinking of a possible solution, not that it passed any sanity checks yet.

I did find some info regarding this topic on some snowmobile forums. There was a particular carb design with a flat slide that was experiencing heavy wear (much more that I've ever seen on a three-wheeler carb). These guys would have all sorts of tuning / idle issues. Their solution ranged from having the slides chrome plated to having different coatings applied. The bottom line though was to build up the slide back to original dimensions to get a better seal.

So what do you think? Am I full of it? If the cost isn't prohibitive, I'm going to try this out... I've got nothing to lose as the carb is just sitting on the bench collecting dust.

[EarlyBronocGuy]

What about using the slide from the new eBay carb in the old, original carb? Measure both, and also the bores of both carbs, you might end up with better fit using the new slide in the old carb.

On another note, consider trying a different CDI to see if runs any different. I fought what I thought was a carb issue (hard to start, idle on when warm, no power, bogging, backfiring, etc) on one of those Chinese buggies (Carter Talon), cleaned and cleaned the carb, replaced the carb, adjusted the valves, replaced the O-ring seal on the intake manifold...I finally grabbed the CDI from my 350x project and plugged it into the buggy (same exact connectors), and problem was GONE. Instantly ran like a champ.

[atc007]

You're on the right train of thought Wonder,but the carb body is also worn away. It's worth trying if you are willing! But <I doubt you'll get the results you're after. Good luck though!

[rodeofan5656]

do i have the same problem?--- when im ridin along, it runs great. and right when i stop it idles normal. then after about 5-10 seconds at normal idle, it idles waaaay down. then back up again, then back down, sometimes dies on its own. when i try to give it gas fast at low idle, it putts and dies. if i ease into the gas, itll idle back up. it does this both cold, and when its warm. not sure how i could explain it better..

[Scratt]

My big red did that too I ended up just putting a carb I had from my parts 200x and after that it ran great

[wonderboy]

do i have the same problem?--- when im ridin along, it runs great. and right when i stop it idles normal. then after about 5-10 seconds at normal idle, it idles waaaay down. then back up again, then back down, sometimes dies on its own. when i try to give it gas fast at low idle, it putts and dies. if i ease into the gas, itll idle back up. it does this both cold, and when its warm. not sure how i could explain it better..

Your syptoms aren't exactly like mine, but in general, I think a worn slide will cause all kinds of issues at idle (including what you describe). My thoughts are that this is where the slide is supposed to be restricting the airflow the most. If the clearances are all jacked, then air will flow around the sides of the slide, instead of primarily under it (through the gap below it). I don't think that the looser tolerances cause issues once you start opening up the throttle because the small amount of leakage is a tiny percentage of the total airflow once the throttle is opened.



What about using the slide from the new eBay carb in the old, original carb? Measure both, and also the bores of both carbs, you might end up with better fit using the new slide in the old carb

You know, I can't remember if I thought to try that or not back when I did the swap. Now I'm going to have to go back and see if they are compatible (remember, the e-bay carb is very similar, but not identical). Like 007 says though, the body is worn too.

I measured the opening and the slide today. Unfortunately, I didn't use the proper equipment (a micrometer and a telescoping gauge) but I did use a pretty nice digital caliper and got pretty consistent readings. What I found is almost exactly 0.003" difference between the diamter of the carb slide bore, and the slide itself. HOwever, this was measured at the top of the slide bore opening (the part that only gets rubbed when the carb is wide open). Using the caliper, I didn't have a way to measure where the real wear point would be, deepest down in the carb body, but I figure it can only get bigger. So with 0.003" difference in diamters, that gives a 1.5 thou clearance at the tightest point. It should only get looser at the bottom. I'll have to figure out a way to properly measure at the bottom of the bore (see if I can locate the right tools at work). Anyway, I may just try this and see what kind of results I get as long as the coating process isn't too pricey.

[wonderboy]

Found some interesting reading today (item #2 in the link below):
http://www.amr-of-tucson.com/carb_facts.html

and then there is this place (don't think I'm going to drop the $90 for his service though):
http://www.amr-of-tucson.com/carb_facts.html
(read the text after the picture)

It's all interesting, but I think unless you are very sentimentally attached to your carb, once it gets to this point, it is a goner... unless I can find some cheaper repair alternative.

[shortline10]

I deal with this issue allot and it can be tricky or sometimes seems impossible to fix but for the most part its usually the slide and or bore that's worn or sometimes its as simple as an adjustment of the needle valve . A worn or partial clogged idle jet can cause this also .

[atc007]

do i have the same problem?--- when im ridin along, it runs great. and right when i stop it idles normal. then after about 5-10 seconds at normal idle, it idles waaaay down. then back up again, then back down, sometimes dies on its own. when i try to give it gas fast at low idle, it putts and dies. if i ease into the gas, itll idle back up. it does this both cold, and when its warm. not sure how i could explain it better..

You probably have the same problem. But,,you can try,,cleaning the carb,,making SURE the pilot is Clean! Seeing a round hole of light thru it. AnD,,replace your intake O ring. if it's still sick after adjusting the idle air screw to it's happiest point. It's junk. but I think you need more tuning than replacing.. Hopefully