Popping rolling off throttle

[Edgejumpr]

Hi Everyone.

So I found a 99 VS1400 that was orphaned. It set up for a few years. I brought her back to life and I got legal last week after the DMV decided to open with or without the beer virus. I rode about 60 miles for the first time yesterday and this has me scratching my head.

After it gets up to temp, maybe 5 miles or so, as I roll back the throttle, pull the clutch to shift, I get a Loud Pop, smaller pop- pop. Under power, no pop. Pull the clutch in while under power, no pop. Its only when its at temp and I roll back the throttle and shift.

Background on the revival:
Prior owner installed what looks like Cobra pipes.
Carb was never jetted.
A/F mixture was never drilled/exposed.
Ran some type of foam air filter.
Carbs were filled with varnish.
Tank had rust.

I relined the tank, installed new OEM fuel lines, petcock, installed K/N filters, fuel filter, exposed A/F mixture. Installed Carb rebuild/jet kit from 6+Sigma and followed the instructions to the letter based on the info I provided.

I took the baby step and only drilled out the side hole and shimmed the needle with 2 shims. It fires up without the choke. Actually the choke bogs it down. I changed plugs and new battery.

When cold, when I first crank, I get a small pop- pop when I roll the throttle maybe 1/4 " just above idle.

I am in Alabama. 225' above msl. 13,600 miles on the bike

Is it just the pipes?

Thanks--- Edge

[Machman]

Good luck. I am playing with a new 2007 with 400 miles on it and cant get it to run worth a shite. I just had the carbs off and everything looked good.
The only thing that I can think of that would cause your popping would be a rich condition on deceleration. Then again these diaphragm carbs are a different animal. You have done some mods so I cant really contribute anything because I dont have a good baseline even with my own bike being stock and not running properly.
Im in Alabama too (Huntsville) btw.

[navigator]

Many things cause this condition.
Tuning without a clue is one...rejetting, pipes, slide drilling, A/F adjustment, carb sync to name a few.
Start with the basics. leaking at the exhaust gaskets at the head?

[hillsy]

Good luck. I am playing with a new 2007 with 400 miles on it and cant get it to run worth a shite.I just had the carbs off and everything looked good.
The only thing that I can think of that would cause your popping would be a rich condition on deceleration. Then again these diaphragm carbs are a different animal. You have done some mods so I cant really contribute anything because I dont have a good baseline even with my own bike being stock and not running properly.
Im in Alabama too (Huntsville) btw.

Can I ask if you cleaned the carbs? You need carb cleaner and compressed air otherwise you are wasting your time - especially if a bike has been sitting for a long time. There will be crap or varnish in the carb orifices that you will not be able to see.

[Edgejumpr]

Many things cause this condition.
Tuning without a clue is one...rejetting, pipes, slide drilling, A/F adjustment, carb sync to name a few.
Start with the basics. leaking at the exhaust gaskets at the head?

You nailed me. I didn't have a clue. I didn't mean to brag. It was a honest effort to bring a bike back to life after the previous Owner let it rot. Re-read my post and understand I didn't try to uncork this bike. I inherited all the add-ons and tried to do what should have been done with some help on this site and advice from a local shop. I know a hell of alot more now. And your advise didn't help.

[Herb]

Considering what you said has been done I am going to list a few things that are not mentioned.
1. Have the carbs been sync'd?
2. have the idle needles been adjusted?
3. If they have you have a lean condition on one or both cylinders or an exhaust leak. Possible at the head or where the header pipe and the muffler meet. Exhaust leaks at the head are common with aftermarket exhaust because most people don't install new gaskets.
4. idle may be set too low or too high.
5. The coast valve(s) may not be working properly. It is supposed to add fuel under high vacuum to prevent the popping in the exhaust.
6. Can you tell if it is only on one cylinder or both, if it is only one, which cylinder is popping?

[Edgejumpr]

Hey Herb.
Thanks for the feedback.
The carbs were synced by sight, not vacuum. I'll dig into that this week.
A/F screw was set according to 6 Sigma. I'll run a few miles and see if an adjustment works.
I checked the exhaust leak with wd-40 at operating temp and it didn't pop or bog down.
I had no idea about the coast valve. I'll check that into that.
I did set the idle low. I'll check that with the other trouble shooting taking one step at a time.

You da man!
Edge

[hillsy]

I checked the exhaust leak with wd-40 at operating temp and it didn't pop or bog down.

That only works for vaccum leaks on the intake side - it won't do anything on the exhaust side.

[Herb]

Hey Herb.
Thanks for the feedback.
The carbs were synced by sight, not vacuum. I'll dig into that this week.
A/F screw was set according to 6 Sigma. I'll run a few miles and see if an adjustment works.
I checked the exhaust leak with wd-40 at operating temp and it didn't pop or bog down.
I had no idea about the coast valve. I'll check that into that.
I did set the idle low. I'll check that with the other trouble shooting taking one step at a time.

You da man!
Edge

Improper sync will cause all kinds of problems from the one you are having, to poor fuel mileage, poor performance, fouled spark plugs, and, if bad enough, hard starting.

[Herb]

Hey Herb.
Thanks for the feedback.
The carbs were synced by sight, not vacuum. I'll dig into that this week.
A/F screw was set according to 6 Sigma. I'll run a few miles and see if an adjustment works.
I checked the exhaust leak with wd-40 at operating temp and it didn't pop or bog down.
I had no idea about the coast valve. I'll check that into that.
I did set the idle low. I'll check that with the other trouble shooting taking one step at a time.

You da man!
Edge

Improper sync will cause all kinds of problems from the one you are having, to poor fuel mileage, poor performance, fouled spark plugs, and, if bad enough, hard starting.

Because of a thread on the 800 forum I thought of another possible issue. Have you checked the slide diaphragms for leaks? leaks on the diaphragms will cause the slides to not move as quickly as they are supposed to and they will return faster than they are supposed to.

[Edgejumpr]

I took a knee and went to the local Suzuki shop for expert help. They noped right out because they only work on 10 yr or less. The sync is right, but the exhaust studs were lose. Way lose. I cranked her cold with soap bubbles and she was burping out of the forward cylinder. I eased down on the studs. If she still backfires, I will get new crush gaskets. Step 2 after that is back to the carb's. Slide/backfire diaphragm.

Thanks for the help.

Edge

[hillsy]

Those exhaust gaskets are usually one use only (a bit like a head gasket). You might get lucky with nipping them up but it would be best to factor in new ones if the old ones have been leaking.

[Edgejumpr]

Thanks for the advice everybody. I got about 5 miles in this afternoon before the rain shut me down. After tightening the studs, it looking like it was an exhaust leak. I'll know for sure Friday. Once again, thanks for helping out a new guy!

Edge