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2002 Nevada carb tuning issues

guzzisti91

Tuned and Synch'ed
Joined
Feb 2, 2018
Messages
79
Location
Villawood
Hello all, first post here. I bought a 2002 Nevada 750 club from a couple on a farm. I can't seem to get the idle right, as after a ride it either races to 2000rpm if i turn the idle screws 180 degrees clockwise or constantly stalls if i turn it back 180 degrees. It also surges badly in 1st, not too bad in 2nd & runs smoothly from there. It appears they may have had a major accident on it, & they did a poor job trying to fix it, so as a result i reset the carbs, bought an anologue carb sync tool & tried to fix the problem myself.

So far, i have adressed the sealing problem (the left intake wasn't connected), cleaned the carbs thorougly, changed the air filter in favour of one i made from filter foam, stopped it from backfiring, & reduced it's surging to 1st & 2nd gear. They idle in sync last time i checked, but i have yet to check it again. The fuel screws have been turned an extra 180 degrees (totaling 360) & this reduced the surging, smoothed the vibration & delayed the stall to 30 seconds. There are also shallow indents on the slides, the needles are set to the 4th notch (i dare not touch it), & when resetting i had to turn those fuel screws a lot.

I work in Blakehurst, & i would take it to Motociclo in St Peters, but they will charge $110 per hour. I also think the humidity may play a part, too.
Any ideas?
 
Tuning carbs via the internet is impossible, but I'll give you a few suggestions. You say the idle sync is good. Make sure you have about 3mm of play is available in the control cables and there is no binding. Check for vacuum leaks. Those will play havoc in getting a good setup. A home made filter can be part of your problem. If the stock airbox is present, get the correct factory filter. You didn't say which way you turned the idle mix adjusting screws, or how far they are from closed. That information would help. Get the DelOrto tuning manual. It can be found online. It may help you to understand the interplay between jetting, needle position, and atomizers. The shallow indents on the slides you talk about are curious. Are you you taking about the cutaway at the bottoms, or actual intents on the sides. If indents are on the sides, these could be a good part of your problem as it may allow extra air around the slide instead of under it.
 
Tuning carbs via the internet is impossible, but I'll give you a few suggestions. You say the idle sync is good. Make sure you have about 3mm of play is available in the control cables and there is no binding. Check for vacuum leaks. Those will play havoc in getting a good setup. A home made filter can be part of your problem. If the stock airbox is present, get the correct factory filter. You didn't say which way you turned the idle mix adjusting screws, or how far they are from closed. That information would help. Get the DelOrto tuning manual. It can be found online. It may help you to understand the interplay between jetting, needle position, and atomizers. The shallow indents on the slides you talk about are curious. Are you you taking about the cutaway at the bottoms, or actual intents on the sides. If indents are on the sides, these could be a good part of your problem as it may allow extra air around the slide instead of under it.

The indents are on the bottom. The problem was worse with the factory filter, & the home made filter is basically a sheet of unifilter filter foam the size of the airbox using the rubber of the old filter as a gasket. But i am missing the front spring on the airbox & tied it shut with string. This appeared to have no negative effect. Problem with air leak theory is that with it's current setup it idles no faster than 600rpm unless i turn them in 180 degrees, upping it to 1100, then it runs away to 1800 to 2000 when i go for a ride. This happened even when the fuel screws were at 180 degrees with the grimy factory filter, & i nearly hit a van during that run. Another problem with factory filters is that they are problematic to install & are pricey, so i opted for the foam. The throttle slack is at a mere 1-2mm, so i will try to loosen it up a bit. The cable sheaths are also a little bent, but the throttle rolls on & snaps back smoothly. I have ordered new cables just in case. But, would it hurt to turn the fuel screw out some more?
 
I turned the screws counter clockwise, & go by degrees because "turns" often mean different things to different people. The fuel screws are 2 180 degree turns from fully closed. I think the idle screws are about 10 or 12 180 degree turns out. I never set them to fully closed
 
OK on the mix screws, they can vary. Usually mix screws are 1.5 to 2.5 turns from bottomed. One turn out and you may be a bit lean unless the pilot jet size had been increased. For the idle speed screws, only turn them in after raising the slides. If you don't the screw will eat into the slides giving you indentations into the bottom edge of the slide. The bike should idle 1000 to 1100 rpm when warm. If you set the idle speed on a cold engine, it will increase when hot.
 
OK on the mix screws, they can vary. Usually mix screws are 1.5 to 2.5 turns from bottomed. One turn out and you may be a bit lean unless the pilot jet size had been increased. For the idle speed screws, only turn them in after raising the slides. If you don't the screw will eat into the slides giving you indentations into the bottom edge of the slide. The bike should idle 1000 to 1100 rpm when warm. If you set the idle speed on a cold engine, it will increase when hot.
Can you please explain what you mean by turns? Is it one end to the other, or a full revolution?
 
1 turn is a full revolution, your 360 degrees.
Danke schon. & thank you very much for the advice. Everyone's telling me to get rid of it because of this, hehe. But hondas with dual carbies often have the same issue. As with the turns, that would probably explain the surging - it makes a similar noise when it runs out of fuel. While i don't think it's a vacuum leak, i won't leave any stone unturned. Any advice on how to check that?
 
This is what the right floats look like. The left ones are ok & both have the same amount of rise & fall. The last owner or the mechanic they took it to appeared to do a messy job, but there are no holes or cracks
 

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Get the DelO'rto carb manual. It tells you how to measure float height, and that is done with the carbs off the bike. Word of warning, those white floats become heavy over time so check their weight. They are the 10 gram floats I think but should be marked.
 
UPDATE: I rebalanced the carbs thinking the surging was a synch issue. I also tried holding the throttle open a bit in order to sync the cables, as i got the idle right rather quickly. I then saw the threads start to tilt as the they became more exposed, so i therefore tilted the carbs 20 degrees toward the airbox as i fiddled with the cables. Couldn't quite synch the cables right. I remembered that the right cable sheath is actually pretty bent, so i thought i might need new cables before i could truly fix the problem.

Nearly an hour had passed, & i had to meet someone to ride with an hour later. So, thinking i had isolated the problem, i put the bike back together & set off. Bike then acted wierdly....

It now idles around 800-900, but runs away to idle at 1100-1200rpm when stopping at lights. Quick blip settles it down to hover around 1000. Otherwise, it settles by itself after about 10 seconds. Oh, & here's the wierd part - the surge is gone. These efforts were enough, strangely. It's acting so normal it's wierd to me.
Success!
 
Threads may be worn in the carb tops and need replacing. It also sounds like new cables would be a good idea. Carbs should be vertical and not tilted, but whatever works.
 
Threads may be worn in the carb tops and need replacing. It also sounds like new cables would be a good idea. Carbs should be vertical and not tilted, but whatever works.
The threads in the tops tilted because they were nearly outside the carb tops & the cables were pulling them in as i had loosened them too much. I fixed this issue by lifting the tank & pushing them upright before screwing them back in. The cables are going to take a while to arrive, & wierdly on the Nevadas, the chrome panels along the tank won't go on properly unless you tilt the carbs. That model Nevada is notoriously tight below the tank, yet it came with upright boots. In fact, they were tilted when i bought it. Ideally, carbs should be upright, which is what i thought before turning them upright in the first place. But then again, bikes often tilt.
Anyways, the issue i speak of here, those on the other forums who had a similar problem didn't end up resolving the issue, but, by the grace of God & a bit of perseverance, i fixed the problem. I only hope others take my experience on board & see if it works for them. Now to see what happens when winter comes, hehe.
But, i digress. Thank you so much for the advice. That revolution info made a big difference. Let's hope i never have to pull those things apart again. Petrol stinks!
 
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