Backfire through the carbs?

[Muleears]

When my bike is started cold, as it warms it sounds like it is backfiring through the carbs, not real loud just a kind of cough sound along with a miss. I've noticed it doing this also after its warmed up and I'm decelerating. As when slowing to a stop, throttle closed, brakes applied, I occasionally here this *cough* sound. I'm assuming this is a carb or timing problem? Any input is appreciated.

Took a little ride this evening in 43* weather. Brisk but easily bearable without any electric assistance. I think I'll plug in my gloves when it dips into the 30's...

[Mr Jensee]

Have you ever checked to see if the spark plugs in the bike are the correct ones? colder plugs can lead to unspent fuel igniting in the exhaust pipes. I would pull them, check to see if they are the correct plugs and check the gaps. If the plugs are too sooty and not light brown in color then it they are not burning the fuel properly in the combustion chamber. Also check the plug wiring for cracks. Aging plug wires could also mean there is not enough electricity to give a proper spark.

[Muleears]

Have you ever checked to see if the spark plugs in the bike are the correct ones? colder plugs can lead to unspent fuel igniting in the exhaust pipes. I would pull them, check to see if they are the correct plugs and check the gaps. If the plugs are too sooty and not light brown in color then it they are not burning the fuel properly in the combustion chamber. Also check the plug wiring for cracks. Aging plug wires could also mean there is not enough electricity to give a proper spark.

Thanks Mr. Jensee, I will do that this weekend. I know the plugs only have 2K miles on them anyway, but I don't know the heat range as I didn't put them in.

[Mr Jensee]

If that checks out ok, you might try a different grade of gasoline or if you are getting fuel from the same location, could be the gas is bad. Change stations and add a fuel additive like Seafoam to see if that changes anything. I have not had to mess with timing on a bike since I had my 79 Suzuki. I suspect newer bikes have self regulating timing now. Carl Leo would have some insight on the Voyager XII. I would give him a shout out.

[Muleears]

If that checks out ok, you might try a different grade of gasoline or if you are getting fuel from the same location, could be the gas is bad. Change stations and add a fuel additive like Seafoam to see if that changes anything. I have not had to mess with timing on a bike since I had my 79 Suzuki. I suspect newer bikes have self regulating timing now. Carl Leo would have some insight on the Voyager XII. I would give him a shout out.

I use SeaFoam every other tank or so. I've been buying gas at different places, but the current tank is from a station that sells pure gas, no ethanol. I didn't get to the plugs this weekend though, I'll try to do that soon. I'll report back when I figure out what plugs I have in it, maybe they are the wrong ones...

[ekap1200]

check all your basics, plugs , wires , look for intake leaks. drain your carb bowls , and check carb sync. Cold weather riding , change your oil to a 10-40 weight. Is this a Cal model with carbon canister? Without hearing it or driving it, I would look at carb sync, or the engine oil is to heavy, if I was not sure its popping back thru the carb's. Perhaps an intake valve hyd lash adjuster is sticking, to make it pop back into the carb. Some recommend adding seafoam to the engine oil for a short period and run it up to temp, then dump it with fresh oil. Let us know what your plugs look like when you get to them. Backfiring thru one of the carb's would to me, indicate a sticky valve train, a minor stumble (cough) and miss would be a different story and I would look at the sync of the carbs first, after checking plugs,wires,caps. What had been done to the bike prior to its problem ?
Gene K.

[Muleears]

check all your basics, plugs , wires , look for intake leaks. drain your carb bowls , and check carb sync. Cold weather riding , change your oil to a 10-40 weight. Is this a Cal model with carbon canister? Without hearing it or driving it, I would look at carb sync, or the engine oil is to heavy, if I was not sure its popping back thru the carb's. Perhaps an intake valve hyd lash adjuster is sticking, to make it pop back into the carb. Some recommend adding seafoam to the engine oil for a short period and run it up to temp, then dump it with fresh oil. Let us know what your plugs look like when you get to them. Backfiring thru one of the carb's would to me, indicate a sticky valve train, a minor stumble (cough) and miss would be a different story and I would look at the sync of the carbs first, after checking plugs,wires,caps. What had been done to the bike prior to its problem ?
Gene K.

When I bought it last January I had the carbs rebuilt by a "motorcycle mechanic" recommended by my son in law. I think he was more of a Harley guy and maybe not familiar with the 4 carb setup we have. I do not know if the carbs were ever sync'd. The tank had some gunk in it, so he removed it and cleaned that out. I'm wondering if he didn't get it all and maybe some of that "gunk" made it to the rebuilt carbs, I should probably check the fuel filter too. I must check the plugs, finding time during daylight hours is the problem... Thanks for all the advice, as soon as I can I'll check all this out. I probably shouldn't complain, once the bike is warm, it runs well, just has that occasional cough and only fair (34-36) MPG.

[carl leo]

on a regular basis i deal with carb "rebuilds" that are laughable. some attempts make matters worse and in some cases are dangerous. just because a "mechanic' has had his fingers in your baby's carbs does not guarantee you got your moneys worth.

[Muleears]

on a regular basis i deal with carb "rebuilds" that are laughable. some attempts make matters worse and in some cases are dangerous. just because a "mechanic' has had his fingers in your baby's carbs does not guarantee you got your moneys worth.

I strongly suspect you are correct. The next person to touch my carbs will either be me (I've rebuilt a car carb or two...), or you (if you still do such things!)

[Muleears]

I've done a little tooling and here's what I found:

Old Plug model


New Plug model


Plug removed from cyl. #1


Plug removed from cyl. #4


These plug have about 2,000 miles on them. The new plugs came from the local Advance Auto who only had two in stock, hence I only replaced the outboard plugs. Any comments on the condition of the plugs? I started it up in a dark garage and didn't see any spark leakage around the plug wires.

[ekap1200]

once the bike is warm, it runs well, just has that occasional cough and only fair (34-36) MPG.

An occasional cough is far better than a backfire thru a carb any day.

[carl leo]

plug 1 looks rich, plug 4 looks lean......carb idle air mix wrong and probably out of sync..

[Muleears]

plug 1 looks rich, plug 4 looks lean......carb idle air mix wrong and probably out of sync..

My next steps would then be to? Replace the other two plugs and get the carbs sync'd? Or should I just bite the bullet and get another rebuild by a competent tech? Your input is much appreciated.

[Scott-(Altoona, PA)]

Your BEST bet would be to remove them and send them off to Carl in Florida. Your best "competent tech" can at best only hope to be a fraction as good as Carl with a Voyager XII.
I mean no disrespect to any mechanics, I don't mind twisting a wrench myself but I also know that there are limits and an honest man knows when someone else is better at something then he/she should be the chosen source.

I'd like to reference ekap1200's signature line for situations like this.
"Its not bad if you don't know something, but when you don't know you don't know; That's when your in trouble". Joe Place 1912-2008

[Muleears]

Your BEST bet would be to remove them and send them off to Carl in Florida. Your best "competent tech" can at best only hope to be a fraction as good as Carl with a Voyager XII.
I mean no disrespect to any mechanics, I don't mind twisting a wrench myself but I also know that there are limits and an honest man knows when someone else is better at something then he/she should be the chosen source.

I'd like to reference ekap1200's signature line for situations like this.
"Its not bad if you don't know something, but when you don't know you don't know; That's when your in trouble". Joe Place 1912-2008

I'll give Mr. Leo a PM and see if he is interested. I wondered if he was still in the business or not.