backfire when cold

[JellyBelly]

So a few days ago my 78 started not responding properly when throttling. when going to ride the best way to describe it it's..like it was getting gas then not then getting gas and so on until it warmed up.

During this time it also decided to start back firing. ..loud with sparks.

but when the bike warmed up riding for 5 mins it would run normal.

Ive decided to run some Gumout fuel sysytem cleaner through it which is meant to deal with rust and corrosion, fuel injectors, intake valves, and combustion chamber.

What do you think could be my problem? Could be a lean/rich problem. I haven't looked at spark plugs yet. Just looking for some input.

Including a pic...for fun I threw on some short pipes (after all this started) which has obviously affected my power and it'll do small pops on down throttle...why you ask...Cos one backfire threw my muffler off and i couldn't tighten it enough to stay on.

[Placerville]

First, don't start pouring things into your fuel system in hopes that it will somehow 'clean something out'. It's just not the way to go. Strong fuel system cleaners can loosen otherwise dormant, solidified debris and spread them throughout your system causing additional problems. Start with your fuel system and proceed methodically through it. Don't jump around with a, "Maybe it's this and maybe it's that, approach. If you do, you'll drive yourself nuts.

You said, "SNIP...it was getting gas then not then getting gas and so on until it warmed up." From this, let's look at fuel starvation. Start with your fuel cap, then your tank, petcock, fuel lines and filter and then to your fuel pump. Once you eliminated these as a possible source, you can move on to other possibilities. Again, don't jump around.

Start by removing your gas cap. Take off the rubber gasket and drop the cap into a jar of vinegar for 3 days. When it comes out, it will be spotless and the (important) air vent will be clean. While that's soaking, drain down your tank and inspect it for rust. If you see any, you can do a very effective 'in the frame' cleaning by using either Citric Acid (very inexpensive) or Evapo-Rust (expensive, but with a multiple-use life span.) Also, remove your petcock and rebuild it. If you haven't done it in the last 3 years, you should. When the rubber 'directional' gasket starts to deteriorate, they can be a major source of fuel flow issues.

Run an old speedo cable (or other flexible wire) into your tanks main and reserve tubes to ensure that they're clean. Replace your fuel lines and filter unless you're positive that they're clean and in good condition. Last, inspect your fuel pump. If it's leaking from the weep hole, replace it. If not, remove the top and inspect to see if any foreign matter is clogging the valves or ports. You can test the pump for correct flow by referring to your Honda shop manual.

You can do all of the above with little expense. After you're sure your fuel system is clean and performing properly, you can move to other possibilities knowing that you've eliminated fuel flow and contamination as an issue.

[JellyBelly]

Good ideas. I rebuilt the carbs and petcock about 2 1/2 years ago. Cleaned fuel tank etc. I'll look at fuel pump but I think I replaced it 1 year ago...maybe that was on the 77. I'll have to look and see.

[JellyBelly]

It still has me baffled. I can start the bike first time every time. It will idle perfect. It will even ride perfect...BUT it has to warm up for 5 mins. Try to ride it before then and it will backfire and not respond to the throttle correctly....going a little crazy.

[JellyBelly]

Don't worry. Sold it to another wingnut.

Got a 2000 Valkyrie to ride now.

[HawkeyeGL1200]

Don't worry. Sold it to another wingnut.

Got a 2000 Valkyrie to ride now.

Definitely one way to take care of a problem motorcycle

Love the Valkyrie!