[nomaders]

Hi Everybody,

I'm hoping that somebody can help me out.

I just bout a used 1988 - 883 Sportster with a S&S Supercarb.

When I start my bike up it runs good for about 5 minutes with the choke on. Then for a period of about another five minutes it runs like ****. Wants to conk out, backfires, ... The choke helps but it still runs like ****. After about another 5-10 minutes of emabrrassing misfires ... it runs great.

I just had the plugs, oil, and air filter changed.

Has anybody seen this? Any ideas?

Thanks,

Nomaders

 

[KevSumac]

My 2001 Sportster does the same thing....I just assumed she's a cold natured bitch.

 

[nomaders]

I have noticed that if I open it up a bit it will warm up faster and not give me a hassle. I guess it just wants more speed....

I'll keep looking for an answer and I plan on taking it in to a mechanic too see if what they say.

Somebody also told me to spray some ether in-between the intake manifold and carb to see if there is a bad intake manifold gasket.

 

[CB750F]

That will work but I wouldn't use ether though. Use carb cleaner, it's much less flamable.What happens is when you spray carb cleaner there if temporarily seals the leak, even for a few seconds. When it hits a leak the engine RPM will change (either up or down).

 

[nomaders]

Thanks, I'll try the carb cleaner

 

[BH121869]

Hi Everybody,

I'm hoping that somebody can help me out.

I just bout a used 1988 - 883 Sportster with a S&S Supercarb.

When I start my bike up it runs good for about 5 minutes with the choke on. Then for a period of about another five minutes it runs like ****. Wants to conk out, backfires, ... The choke helps but it still runs like ****. After about another 5-10 minutes of emabrrassing misfires ... it runs great.

I just had the plugs, oil, and air filter changed.

Has anybody seen this? Any ideas?

Thanks,
Nomaders

On my 2001 1200 Sportster I pull the choke out to give me about 1000 RPM's or so and she fires up right away and I can pull out right away but usually give it about one minute to get the oil all through everything. It does romp like a dragster till I push the choke in. That only takes two minutes and she is ready for anything. I always have the choke in within three blocks or so.It never backfires or does as yours is doing. My first guess was the leak somewhere in the mixture flow and I have used starter fluid. The carb cleaner will work as others said too. I'd for sure have it checked out. Timing is a second thought but it would require something else also to do as yours does. My carb is stock and i don't know about the S&S. My third thought goes to the carb. Are you running 92 octane? Try a fuel addative like STP. I have had two bikes that would not run their best without it. It only takes a small amount as the container is for a 20 gallon tank. Good luck with it.

 

[nomaders]

Thanks for the input...

Timing is a second thought but it would require something else also to do as yours does. >> Yes, I figured it would be a problem during and after the warm up but always a posibility

My carb is stock and i don't know about the S&S. My third thought goes to the carb. >> Yep, one of the last resorts and I'd take it in for that

Are you running 92 octane? >> Yes, I'm using 92 octane

Try a fuel addative like STP. >> Sounds like a good idea. I'll try this after the carb cleaner

Good luck with it. >> Thanks

At the moment my wifes bike has some issues (she's just learning, it's a Lifan 250, very similar to a Yamaha 250, Virago). Her bike is only running on one cylinder so I need to get it going again before I continue to troubleshoot mine. I'll post back after I try some of the tips.

 

[nomaders]

OK, the Lifan 250 is back on the road again so I can continue to troubleshoot the sporty.

1) I changed the air cleaner and the old one was horrible. It was an older one and the foam just about fell apart in my hand. I bought a new one and the filter is contained within a metal fence and was pre-oiled.

2) I've been adding the STP gas treatment. So far I used one container.

3) Every now and then I spray the carb with carb cleaner.

4) When the bike was running I sprayed the between the carb and intake manifolds with the carb cleaner. No noticeable change in RPM's.

The bike has been running much better, not perfect, and likes to "burp" every now and then. I'll need some more time to eliminate one variable at a time and see if I can pinpoint the exact issue. Maybe it'll be fine and I won't need to worry about it

Also, at winter approaches, I'll take it to a good shop for an inspection.

 

[buellosaurusrex]

Does your S&S have an accellerator pump? You're running a butterfly valve carb with a motor that is sensitive to manifold pressure (vacuum) changes. I had a similar issue with the stock CV on my Buell; changing over to a Mikuni HSR42 flat-slide with every circuit tuneable was the best investment I ever made. It sounds to me like you've eliminated the idea of an intake manifold leak. What do your plugs look like when the problem exists? Plug coloring will tell you a lot.
I've used a Gunson ColorTune with some success in troubleshooting carb problems as well; you can actually see the color of the flame when the motor is acting up which will give you a true picture of what's going on in the combustion chamber.

 

[nomaders]

Hi Bu...,

Thanks. I'll pull the spark plugs and check it out and also check the vacuum situation. This bike is fairly new to me (approx 2 months or so) so I have a steep learning curve.

The good thing is that I'm in no rush

Regrds,

Nomaders

 

[buellosaurusrex]

I don't mean to bang the Mikuni drum so loud, but I screwed around with the stock CV-40 to no avail and went to a CV-40 with a Thunderslide kit, which was much better, but both still had the "Keihin Cough" which never went away until I slapped on the HSR. For what you spend trying to upgrade carbs, it's not even worth the effort. If you do the T-slide and Yost Power Tube, you've got more than the price of a new HSR into a CV carb. On your 883 you can order the stock Sporty HSR and it'll probably run great right out of the box. The nice thing on these carbs is you don't have to pull the carb OR THE BOWL! to change main jets.....they put a nice l'il plug in the bottom for you. Plus, it is so freakin' tuneable! Accelerator pump stroke, duration, everything is adjustable for your motor. You can get great buys on eBay as well.
S&S makes a great product, but for the Sporty Evo motor I think the flat slide carb out-performs a butterfly-valve carb hands down. This is pretty much a fact on the tube frame Buells which use the Sportster-based 1200 motor....I've seen the dyno sheets to prove it....and my own "butt-dyno" can back it up.

 

[buellosaurusrex]

Oh yeah...also, if your S&S uses a "choke" valve (as opposed to a true "enrichener circuit", which adds more fuel instead of restricting airflow to richen the mixture,) that could be the root cause of your warm-up problems. Look down the carb throat and see if your choke circuit opens and closes a butterfly valve in the venturi.

 

[nomaders]

Bu... Thanks for the info. I had to do a bit of research after your last posts

OK, here's where I am right now ...

1) It's an "E" type S&S carb.
2) It does have an accelerator pump.
3) The choke does not move the butterfly valve.
4) I pulled the spark plugs and they're a bit blackish. I think this is due to a rich gas mixture.

Saying all of that I read through the S&S installation manual and realized the following:
- I pulled the choke up too high(rich mixture) and kept it on for too long. I should've turned it off much sooner then I did but since I was burning so rich it didn't want to idle after I turned it down.
- Also, I think the accelerator pump needed to be turned down a bit

So far with these adjustments, it's doing much better, not perfect but better.

After 20-30 miles I'll check the spark plugs. If they look better I'll replace them with new ones and see what happens.

Regards,

Nomaders

 

[buellosaurusrex]

Good to know. Let me know if you have any more problems......I'll help if I can.

 

[SgtRob]

Pull the plugs out and "read them". If they are ash white the engine is running too lean. This will cause the condition you are describing, and can be caused by several things. Make sure you have the correct plugs for this engine. Is your carb jetted and adjusted properly? Are you using a good fuel in the proper octane rating? If you have changed the pipes and/or mufflers this can cause this. If you have changed your eigine air cleaner, this can cause this as well. Your carb has to be tuned for any of these mods, otherwise your engine is running on too much air and not enough fuel. A simple fix my friend. Just read the plugs. They will tell you the story behind your problem. Hope this helps...