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I bought a 98 superhawk and had the carb rebuilt by a mechanic. He’s got it apart and is showing me some issues on fuel delivery. First it seems as if the Petcock diaphragm is bad and is leaking fuel into the carb when it shouldn’t be and randomly going lean. The vacuum line is on the correct nillle behind the Petcock not on the bottom. He also suspects fuel is getting past the needle seat in the float bowl and dumping fuel into the cylinder as there is a lot of standing fuel after removing the carb. The needle seats are press fit, and we cannot seem to find new ones to install. Am I going to have to buy new carbs to get this solved? Any help is much appreciated. You can call me 209-278-8372 if you are inclined. We’re at an impass.
My experience is, fix the petcock 1st, then run it a few miles it seems that the engine vibration clears out any debris still in the needle seat. I had this happen with 2 different bikes. It's rare that the brass seat goes bad unless water corroded the brass. I would think that with a leaking needle seat it would go rich, not lean.
Let us know what you find.
Thank you for the advice. Perhaps I was unclear on the condition. It is primarily rich with fuel spurting out the brass vents on top of the carbs (mainly the front carb) but when running it seems as if sometimes it will lose fuel delivery altogether. I bought the bike running terrible after sitting for years with fuel in it so I had the carbs cleaned out and rejetted. He installed the carbs without the air box on and ran it to get a baseline and this is when he discovered the fuel delivery issue. The bike has 19k miles on it and doesn’t make any strange noises, doesn’t smoke, and when it does allow us to baby the rpms up sounds strong. The mechanic is primarily a Harley guy so he may not be privy to the ins and outs of this carb setup. Seeing as I can’t find any way to replace these needle seats as they are press fit I am hopeful the diaphragm will help. We’ve ordered the diaphragm and are eagerly awaiting the next step. Also, the tps was at 870 and he has gotten it down to 620. The bike came with a k and n filter and yoshi carbon exhaust. Current tests have been done without the air box on the bike just naked carbs. I’m at 4000 elevation and I believe he went stock on the main jets but changed the pilots. I’ll have to verify the pilot sizes.
Unless you have access to a Dyno, for a long time, these bikes do not run for S*#t without the air box! You mentioned "re-jetted" how so? Replace the petcock diaphragm, install the stock jets making sure the needles are in their respective front and rear orientation, re-install the airbox, including the stacks and the crankcase vent collector bottle, put the lid on it and I bet it'll run fine. Unless it's been dyno jetted, Etc. Some say it's hard to get these bikes to run well with a K&N, but I found a trick that works really well for me. There's a thread (old) on this forum that worked well for me and many others. Some will disagree, but I can only share my experience.
Where are you out of?
Thank you for your help! I’m very grateful for this forum and for you taking time to help me out. When I say rejetted, he went back to stock main jets and I believe he changed the pilot jets one size. The bike was sold to me with the same size jets in both carbs. Since we are at 4000 elevation our thought was to get it to run as close to stock as possible and then see if any adjustments are needed once we get a baseline for it. Anyway, I might not be the best at relaying info. This gentleman working on my bike is not a computer guy, and I’m not much of a mechanic but we’re trying to work together here. I’m in calaveras county California. Bought the bike in Madera. As frustrating as it is not to be riding right now, I’ve learned a lot and am pretty confident I could handle this task next time it needs to be done. We should have the diaphragm kit this week, and I’ll send him pictures of this thread so hopefully he will try it with the air box on. I’m trying not to tell the guy how to do his job just give him as many resources as possible to make it easier on him. Thanks again!
I always tell others how to do their job until they realize I can do it better than they can and they walk away from the task so I can do it myself which is what I wanted in the first place.
I'm going to second the opinion that the needle seats are more than likely not bad. I'd throw a rebuild kit at it first, and tell the hardly "mechanic" to not try and run this bike without an airbox. Here's a pic of the new parts in the kit.
Fresh rubber tips on the new float valves should seal up the flow when called upon. And I personally would just clean and reuse the original needles, given they aren't worn or damaged.
You're just a few hours away. I'm in Orange County. I have friends and family in Bakersfield, Merced, and Fresno. So I ride up there a bit. I'm 65 but I still do 3-400 mile day rides on my Super Hawk. If you're going with stock jetting, Might I suggest a #175 front and a #178 rear main, #48 pilots. A common problem is getting the needles reversed front to rear. I mean the slide needles, the float needles are interchangeable. They have a # stamped near the top. You might want to search the forum for 8451Hawks carb write up. It'll get you headed in the right direction.
I've gone over 120 thru Yosemite to Tioga Pass 9,350' needing nothing more than raising the idle and a half turn in on the fuel mixture screws. Super Hawks seam to run fine a little rich.
If you get in a bind, PM me and I'll see about riding up to help out.
Hey thank you for all the help! I’m in a town called arnold right over highway 4. I’ll be passing along this info. I really appreciate your help. Any idea where I could order an oem air filter. After all I’ve heard about the k and n I’d rather go oem and then once it’s running good if I want to tweak it I can always make adjustments from there. Just trying to get a baseline for this bike.
Great area. My son and I went through there a couple of years ago. Coming from the Bay Area. On our way to the Mono Lake area. We did Highway 4 to Highway 89. To the 395. It was like two or three years ago when they had all the fires. And it was hotter than hell. But, I will never forget it. When you go on a 2700 mile ride with your son. It's something a dad will always remember. I was on my superhawk and he was on his Suzuki sv1000s. It was epic. !
Got word yesterday the mechanic replaced the petcock diaphragm and tested that it was working but still has an overfuel problem. He said it would usually stumble around 6k rpm and had moments of brilliance but overall not running right. Said after his ride he could hear fuel sizzling off and stripped the bike down to the carb to find this going on.
05-31-2020, 06:20 PM
