Loud pop when releasing throttle

[Dchmura123]

Hello friends! I pulled out the boulevard s50 for the riding season and immediately noticed a single loud pop from the rear cylinder exhaust when quickly closing the throttle, only at slow speeds and only when quickly releasing after light throttle. If I'm riding hard and quickly release I hear no loud pop. Last season this was not an issue. I went ahead and did the regular maintenance, new filters (stock suzuki), oil change, and carburetor sync (both idle and throttle sync were pretty far off). Took it for a spin and the single loud pop is still there and exactly the same. Went back twice and checked all the carb boots and clamps everything checks out ok. Any ideas? Exhaust leak at header? Dirty carb? Thanks in advance!

[hillsy]

All other things withstanding it's probably some crap in the pilot jet. Try running some Seafoam through the fuel and see if that clears it up.

[Lechy]

Ah! Seafoam, the grand panacea.
When you did the carb synch, did you re-adjust the AF settings?
[emoji41]

[Dchmura123]

Yes I did also dial in the a/f settings but it didnt seem to make much difference if adjusted richer or leaner.

[Lechy]

Well, if adjusting the AF screws didn't make a difference the most likely culprit would be a partially blocked pilot air jet. Get the bike warmed up, reduce the idle with the black thumbscrew rear carb, adjust the AF on the rear and then the front, one of them should make a big difference to the idle, the other not so much. The one that dosen't is the problem carb. Then check the header bolts for tightness, don't get heavy handed you could shear the bolt. Try spraying some soapy water around the header clamps whilst the engine is running cold.

[emoji41]

[Dchmura123]

Sorry I should have been more specific. When I adjust the a/f screws I do hear the change in rpm and I am able to get that sweet spot with both carbs. I tried leaning then richening the rear carb and the pop when releasing throttle didnt change at all at both extremes. I noticed the rear cylinder header looks like it wasn't tightened evenly. It's easy enough to adjust, gonna go ahead and do that and get back on here with an update. Thanks!

[Dchmura123]

Aaaaaaaand the carbs are out. Gonna give them a good cleaning and see what happens.

[Dchmura123]

Took my sweet time cleaning the carbs last night, second time around isn't bad especially remembering the mistakes made couple years ago when I first cleaned them. Took her for a short ride
and unfortunately the rear cylinder exhaust still has a backfire when completely releasing the throttle (one loud pop). Some more information about the bike: 30k miles, valve adjustment done 2 years back, stock suzuki filters, Vance and Hines slip on, dynojet stage 1. Not sure what the problem is but I absolutely do not regret cleaning the carbs cause it for sure made the bike run much smoother. Any other tips are appreciated!

[hillsy]

Might need new exhaust header gaskets. They are generally speaking a one use only item.

[Dchmura123]

Yea I agree, I'll put an order in tonight and update once its complete.

[Lechy]

If the problem persists, try going back to OEM jetting. The V&H slip-on's didn't require a jet upgrade, just an AF adjustment.
[emoji41]

[Dchmura123]

Will do, Thank you. The dynojet stage 1 kit is very basic, all it asks for is changing the oem needle to the dynojet provided needle, shimming with a washer and changing needle groove position. I did not drill the slide hole like the directions state. What do you think about the dynojet kit? Will it do more harm than good? For clarity here is a link to the directions
https://www.dynojet.com/amfile/file/dow ... duct/3603/

The only thing that stumps me is 2 years on this set up never an issue and the bike runs beautifully! I'll swap the header gaskets and check the plugs, if need be I'll revert back to stock with the carbs.

[Lechy]

Drilling out the sliders is a bad idea, replacing them can be bloody expensive. Only required if you fit free flow air filters. You could try the clip in a different slot on the needles. But it's most probably leaking headers. When you had the carbs out, did you check the operation of the coasting valves?

[emoji41]

[Dchmura123]

I agree, drilling anything on a carburetor is not a good idea in my opinion. The coast valves are clean, in great condition, the rubber is not torn and the spring seemed to be in good condition as well.

[Herb]

Will do, Thank you. The dynojet stage 1 kit is very basic, all it asks for is changing the oem needle to the dynojet provided needle, shimming with a washer and changing needle groove position. I did not drill the slide hole like the directions state. What do you think about the dynojet kit? Will it do more harm than good? For clarity here is a link to the directions
https://www.dynojet.com/amfile/file/dow ... duct/3603/

The only thing that stumps me is 2 years on this set up never an issue and the bike runs beautifully! I'll swap the header gaskets and check the plugs, if need be I'll revert back to stock with the carbs.

I put the dynojet stage 1 kit on my 87 1400 and was not happy with the results. The bike was sluggish on the bottom end and my gas mileage went form 45-50 down to 35-40. The needles in the kit had very little taper and were shorter than the stock ones. I took the stock needles and sanded them with 600 grit sandpaper, reinstalled them with the stock spacer below the clip. I did drill out the slide with the provided drill bit. the bike ran much better and my gas mileage went back up to over 45.

[Dchmura123]

Yea the dynojet kit isn't worth the cost in my opinion.