If it were me I would not go to all that trouble and extra money for a new or different carb. Your cv40 carb is a great carb and for a little money at cv performance get their velocity needle, a 46 idle jet, a 185 main jet, a full gasket kit with intake donuts and carb seal, their good accelerator pump diaphragm. Get two spray cans of berrymans carb cleaner. If your idle speed needle has the lead cover over it cv performance has instructions that comes with the kits that will tell you how to take it out. Clean the carb good and put the kit in and I guarantee it will be right. If you need help we will help you. We will get you right for less than c note. And it will be better than any other carb out there. Cv40 carb is the best for stock or mildly model evo. Sorry for the long post. If I can help I will in any way. You can do it and feel good after you do it.

 

Thanks Tim for the shopping list and the encouragement! I'm always nervous before tearing stuff apart but the financial considerations end up driving me to DIY. Thanks again to all y'all for offering your input.

 

I put a 48 slow jet in (I don't have a 46) for giggles and even with that too large of a jet I can't make the engine stumble even with the mix screw backed >4 turns. I'm wondering if I damaged the seat.

 

On my 2000 the tank liner was peeling and clogging up the fuel filter. So what I do is check the tank every so often, when I see the pieces of liner floating around just spend the time remove the tank and flush it out. It's made my bike run better ever since.

 

Look at the tip of the mixture screw, it will frequently show damage first.... if the tip is damaged, try one of the EZ-adjust mixture screws (they don't need a screwdriver). Be careful not to lose the o-ring and washer at the tip of the mixture screw...!!! I think CV Performance is one of the few places you can buy a new mixture screw packing kit (spring/o-ring/washer by themselves).... As I rebuilt mine, I noticed the tip of the mixture screw was bent a little. I replaced it with one of the EZ-adjust mixture screws and was able to dial in the carb...

The technique for setting the mixture screw is to count how many turns it took to close it, then open it the same amount plus 1/4 turn. If the mixture screw has been messed with and is not in it's stock position, then start around 1 3/4 turns....

Once the bike is warmed up and idling, you're ready to adjust the mixture screw. Turn it in (closed) until the rpm changes and/or the engine starts to stumble... turn the mixture screw SLOWLY... once it stumbles, back it out (open) until it runs smoothly and then add 1/8 turn.

Note: some twin cams will not stumble when you tighten the mixture screw, mine didn't.. in that case, just open 1 3/4 turns and go from there...

When you make a change to the mixture at idle, you'll sometimes need to re-adjust the idle screw. Once the idle and mixture is set, blip the throttle. If it's smooth with no backfiring through the carb, you're there! If it hesitates or backfires through the carb, open it 1/8 turn and check again. Once it's smooth, I take it for a ride to make sure... I'm looking for smooth acceleration and no back firing through the carb from low to mid rpms (in the proper gear of course)...

The proper adjustment is usually between 2 & 3 turns... if you have to open it 3 1/2 or more turns, it's time to bump up the size of pilot jet...

Good luck.. it's a little time consuming, but you'll get there...

For your amusement....... I hadn't rebuilt/tuned a CV40 carb in 15 years when I did mine. After the carb rebuild, my bike was WAAAY rich, and would not idle... I had the carb off 4 times, checking and looking at stuff... I finally just sat there staring at the exploded carb diagram... I just knew I was missing something very obvious... it's like trying to proof-read your own paper... very hard to do... then I saw it, I had installed the needle valve on top of the plastic spring spring holder, instead of under it (I have no idea why)... that's only about an inch higher (more open) than it should have been... felt like an idiot. I turned a 20 minute tune job into a 3 hour frustration.. but I finally got it right!

 

thanks again hattitude for your time. I do have a new ez just screw (love it) I just wonder about the seat being damaged either by me or the previous owner. I've been using the "idle drop" method where it's supposed to flood when you back the screw out. It'll stall when I screw it IN just not the other way. I'll go at it again carefully following your advice.

What's killing me is that when I try to put the idle back to 1k (I adjust at around 800 by ear) it inevitably drops to about 500 and then eventually stalls. So I pull up to a stop and it revs at 1200 or so and then drops to 500 and then quits. It always seems to go to the same 500 place no matter what I do.

Last night was interesting in that it didn't hang as much at high idle but went right to to a too slow idle. Hopefully it's mostly operator error which is fixable. I have all the stuff that was suggested from CVPerformance coming soon so I'll be cleaning the crap out of it.

I read also that you shouldn't adjust mix/idle on the side stand. I'll try the method you outline with the bike upright and see.

Thanks again for your time. I'll let you know how it goes.

 

Just a thought, but make sure when you put your throttle cables on, they aren't fighting each other.... sometimes you set one, then adjust the other too tight, it will fight the one you just adjusted.... it can cause weird idle behavior....

Also idle related... I know you said you dealt with your vacuum fuel petcock. I forgot if you switched it out or just turned the diaphragm around.... but erratic idle can be fuel flow.... make sure the in-tank screen is clear, the petcock is flowing steady, and you capped the vacuum port for the OEM petcock...

Also, I've never used the "back out (open) until it floods" method for finding the sweet spot. Seems to me it would leave it very rich...

Keep us posted...

 

okay, took it out this morning and warmed her up. I think I got the mix by going very slowly. I adjusted the idle speed again very slowly. There is a 1/128 sweet spot where it seems to work it either drops to too slow or jumps to a very insistent idle. I also wonder whether I'm taking so long that the bike is overheating and throwing things off.

 

Haven't been able to get a consistent idle at all. Hangs, then drops then it's high, then it's low. Pulled it and rebuilt it this morning. cleaned the crap out of it paying special attention to the idle circuit. Still hangs. I feel like it should idle after less than a second after letting off not 10 seconds. Also, it's never the same stop light to stoplight.

I had an ironhead with a super b that suddenly started to idle very high. reinstalled the intake 15 times at least trying to cure an air leak I couldn't find. swapped the carb out with the same model from ebay and it ran fine. I think I'm going to pick up either a mikuni ez carb or an aftermarket cv. Otherwise I'm taking it to the mechanic.
I'm at a loss

 

One last thing to try.... are you using an new carb manifold gasket? Next time you install the carb, put some silicone grease on the gasket. I put it on the outside of the manifold where the gasket slides on, and of course on the gasket where the carb pushes into the gasket. You don't need to slather it on, just a nice, thin, even coat. It will ensure that you don't have an intake leak between the carb & manifold.

While the carb is off again, you can inspect the manifold to head connections to ensure they are leak free...

It sure sounds like you covered all the bases... gotta be something simple I'd bet... Just like you can't proof-read your own text, it's hard to check your own work.... do you have friend that knows carbs that can go over your work with you?

Good luck...