1998 thunderbird sport

[kzoorob]

Hey, its been a long time since ive been on this forum but its nice to be back! FYI, my 2006 Speedy is still going strong!

Question i hope someone can answer. My father in law has a 98 Thunderbird sport which he really like but is having trouble with and can't seem to get right.

At idle or at low speeds the tach will dip down and sometimes shut down the engine. He has taken it in twice to two different shops to no avail. One shop replaced his airbox because it had gotten warped mechanic said "probably due to backfiring which overheated the box now allowing fresh air into the carbs." Replacing the airbox helped for a short time but now its as bad as ever. It is also a very warm blooded bike and doesn't like to start in temps less than 80degrees F.

Anyone have any ideas? He would like to keep the bike but not if he can't get it fixed. Thanks guys!

 

[kzoorob]

BTW, he already had the carbs rebuilt, new jets etc.

 

[The Seeker]

It could be the crank position sensor...either it's bad and needs to be replaced or it needs to have the air gap reset. I don't know the specific gap for a Thunderbird, but they should have a certain amount of gap between the sensor and the end of the crank where it senses it spinning. Normally, the gap doesn't change by itself, so I would suspect that the sensor needs replacing which isn't hard to do at all. What lead me to say that is the temperature thing....when they start to go bad, temperature will make a huge difference.

Coils also have a tendency to be affected by temperature when they are getting weak. Engine heat will "fry" them and make them start to act up. Once that's happened, they can tend to not allow the engine to start/run when they become cold.

Lastly....Has he had a look at the sparkplugs?

 

[Lonzo]

May need to back the idle screws out a bit. Was it doing it before carbs were rebuilt?

 

[kzoorob]

Thanks guys for the tips! I'll check with him but i think it was happening before the carbs were rebuilt (which is i think why he had them rebuilt) and i think the plugs were ok but i'll double check. Thanks again!!! I'll keep you posted!