Jetting recommendations
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Novice
Joined: Oct 2014
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From: Cleveland
Jetting recommendations
Hi all. Getting a little carb backfire - suspect I'm lean. Bike is a 98' FLHT stock except for Thunder Header 2 into 1's. Can you put me into jetting range and screw setting range. Thank you for your help.
Outstanding HDF Member
Joined: Oct 2010
Posts: 2,706
Likes: 14
From: Near Frankenmuth, MI
Odds are good you don't need to be changing out jets unless you made some dramatic modifications to the engine.
Air / fuel adjustment is general about 1 1/2 turns out from lightly seated. Sometimes they vibrate out of adjustment. Keep in mind too that it's often located under a little lead seal that has to be cautiously removed.
Check for bad, cracked or loose vacuum lines from the carb to the VOES or the petcock. (not certain if your year used a vacuum operated petcock or not)
One thing about older Harleys that you can count on is intake seal leaks. The rubber seal ring is up against the hot heads and bake until they begin to leak air past them and this offsets the air / fuel ratio making all kinds of issues.
Many use carb cleaner and spray the seals. If the RPMs fall suddenly you know you have a leak. (just like shooting the cleaner in the air inlet while cleaner a running bike)
It could be a few other things but this is where I'd start to figure it out.
Repair is a couple of fresh seals and removing the carb and intake is a bit tricky with a specialty tool to back off and tighten the intake seal rings do to the tight location. I find it's best to pull the tank out of the way and the horn / VOES brace assembly on my ride. Tighten them down, to specs, a little on each side until tight keeps them aligned properly.
Other issues could range from simply a dirty carb or air filter, bad gas line allow crud into carb, cruddy petcock filter, too loose batteries terminals and faltering ignition system.
Hope this helps you do a few checks and get's you back on the road.
Air / fuel adjustment is general about 1 1/2 turns out from lightly seated. Sometimes they vibrate out of adjustment. Keep in mind too that it's often located under a little lead seal that has to be cautiously removed.
Check for bad, cracked or loose vacuum lines from the carb to the VOES or the petcock. (not certain if your year used a vacuum operated petcock or not)
One thing about older Harleys that you can count on is intake seal leaks. The rubber seal ring is up against the hot heads and bake until they begin to leak air past them and this offsets the air / fuel ratio making all kinds of issues.
Many use carb cleaner and spray the seals. If the RPMs fall suddenly you know you have a leak. (just like shooting the cleaner in the air inlet while cleaner a running bike)
It could be a few other things but this is where I'd start to figure it out.
Repair is a couple of fresh seals and removing the carb and intake is a bit tricky with a specialty tool to back off and tighten the intake seal rings do to the tight location. I find it's best to pull the tank out of the way and the horn / VOES brace assembly on my ride. Tighten them down, to specs, a little on each side until tight keeps them aligned properly.
Other issues could range from simply a dirty carb or air filter, bad gas line allow crud into carb, cruddy petcock filter, too loose batteries terminals and faltering ignition system.
Hope this helps you do a few checks and get's you back on the road.
Outstanding HDF Member
Joined: Oct 2010
Posts: 2,706
Likes: 14
From: Near Frankenmuth, MI
Tomfiii,
I understand your comment.
I have successfully diagnosed intake leaks by using the spray method on the intake seals with it always impacting the rpms.
Smoke from the exhaust may be another option, but, if it's sucked through an intake leak why would you think it would not impact the rpms? (just curious)
I understand your comment.
I have successfully diagnosed intake leaks by using the spray method on the intake seals with it always impacting the rpms.
Smoke from the exhaust may be another option, but, if it's sucked through an intake leak why would you think it would not impact the rpms? (just curious)
Road Warrior
Joined: Dec 2007
Posts: 1,666
Likes: 3
From: Styxville
You most likely need to go up to a 46 slow jet and a 180 main jet.
While you have the carb off you might as well fit a CV Performance "tuner kit" to get the best out of the carb. (basically the kit is the above-mentioned jets, plus a new jet needle and a softer diaphragm spring.
And while you have the carb off you might as well put in new good quality (Genuine James etc) intake manifold seals. These bikes are coming up to 20 years old, so anything made of rubber is going to need replacing sometime soon.
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