One plug fouls, 1995 Suzuki 115, exhaust bf

[pcolajoe]

1995 Suzuki 115DT<br />Idle has a backfire thru exhaust about every 6 seconds. The top spark plug coats evenly with a dry carbon coating after a few minutes. I have cleaned all the carbs. Today I took out the idle air screw and spring, and the air jet and recleaned them, and I opened the throttle and sprayed carb cleaner into the idle air jet hole and saw it come out the small hole in the top rear of the carb, so I feel that passage is clear. I also sprayed into the air jet hole and it seemed clear. While idling I lossened the air jet and it speeded up the engine a little, and then even removed it, but it still had the backfire.. I figured that cylinder is running too rich, but I can't find the problem. Has any one encountered this? Joe

 

[rodbolt]

Re: One plug fouls, 1995 Suzuki 115, exhaust bf

hello<br /> check the fuel pump diaphram. a sneeze or cough sound is a sign something is lean. and remember those carbs work backwards on the air jets<br /> screw them IN it gets a richer mix and out it gets leaner.<br /> recheck all the link and sync. usually its a lean condition. <br /> good luck and keep posting

 

[pcolajoe]

Re: One plug fouls, 1995 Suzuki 115, exhaust bf

Thanks Rodbolt for the help. This board and posters like you has been a life saver! I had all ready checked the fuel pump diaphram and it looked good, but I checked about 5 things this am, including the linkage and making the adustment richer. I was going to clean the carb again, but I decided to stick to the easiest things first. I bought some decarbon product that i had read about on the board and tried that as I have never done that. It did get rid of the backfire and it ran smooth again. I took it out in the bay and did about a 15 minute run, and it started to lose power, but stayed on plane as I gave a little more throttle. Then it was ok again, and I returned with no problems, idle speed in the no wake zone for the last few minutes. I will look at that plug again tomorrow, and try a new one and see if it fouls, and see if the engine continues to run well. I only sprayed the decarbonizer into the carbs, I might try adding a product to the fuel for that purpose. Thanks again, Joe

 

[jim dozier]

Re: One plug fouls, 1995 Suzuki 115, exhaust bf

Decarbonizer is for the pistons and cylinder heads not the carburetor. Spraying anything, including carb cleaner, into the carb throat will have no effect on the carb. The potential carb crud is well upstream of the carb throat. I would suggest that you remove the carbs and do a thorough rebuild/cleaning. I may be wrong but I am guessing from your description that your "cleaned the carbs" was inadequate (you would not be the first person). I agree with Rodbolt that you are describing a lean condition. The Mikuni carbs on Suzukis are very sensitive and need to be kept clean (not on the outside, its the orifices and jets that count). They are not complicated. Buy a rebuild kit for each carb, completely disassemble them, clean them with appropriate carb clean, blow them out with compressed air, replace the kit parts, and set the float and air jets to the recommended settings (you have a manual right). If you went to the trouble of looking at the fuel pump diaphragm you should have replaced it, they're relatively inexpensive, you may have missed small holes or perforations.

 

[pcolajoe]

Re: One plug fouls, 1995 Suzuki 115, exhaust bf

Thanks jimd for your thoughts. I sprayed the decarb in, not to clean the carbs, but to remove any carbon build up in the head, I thought I might be getting preignition from carbon build up. At any rate it did end the backfire and the engine started running smoothly. Today, I removed the #1 plug and it was fouled again, all the others were very clean after the decarb. I figured if that one plug fouled, it had to be something in the carb, so I took the carb off and rechecked the float adjustment which seemed just a little off. Jets and bowl were clean. I replaced the gaskets. I reassembled and ran with a clean plug, and no fouling! The idle air jet is set to factory specs, 1 1/2 turns for this model. I know on some engines you have to adjust them, and I did experiment with that when it was not running right, but it did not help. I put in a new plug and will be running it this week, but I feel I am in good shape now. It is very smooth and no fouling of the plug and no backfire. I wanted to post what I did in case someone has the same problem, it might give them a place to start.