Carb tuning

[Arnie]

I recently put foam pods on my bike.  At that time I also bumped the MJ up one size to 115.  Since then I've been getting 'extremely' good fuel economy.  Although others who have ridden my bike think its stronger than their FJ, it seemed a bit soft for roll-ons to me.  I decided to raise the needles 1 washer (0.5mm).  While doing this I found that #4 carb diaphram had a small hole.  I've replaced it and raised the needles as planned.  My roll-on is now sharper and it seems to pull better.  I've not been able to check fuel economy yet.

My question:  Is the improvement due to increasing the richness on the needle OR due to #4 slide now working with the others?

Note: I vac balance the carbs every time I have the tank off and/or if it starts to get vibey.

Cheers,
Arnie

[SlowOldGuy]

Arnie,
When you installed the pods, you mostly leaned out the needle circuit.  I'd say the needle position made the most difference.  Unless you're winding the throttle to the stop, you're not working the main jet that much.  You could change that main back adn probably not even notice any change.

DavidR.

[Arnie]

David,

Thanks for the reply. (just the replyer I was after :-)
When I put the pods on, it was definitely lean.  Changing to the larger MJs did help and I only went back in because the bike was so frugal.  The slight softness in roll-on was minimal and I actually thought it mainly due to losing the airbox.
I do use full throttle, but not too often :-) run out of room pretty quickly.

What symptoms would you notice when the diaphram has a small hole?

Arnie
 

[andyb]

Per FactoryPro the main has some effect on the needle circuit, which makes sense, as it feeds it.

Would be not a surprise to find that the needles could come up a notch and have it feel a bit sharper.  The torn diaphram, if it's a pretty small hole, shouldn't make a huge difference as the revs climb, just some roughness at the edges.  Bigger hole would make a bigger difference, of course.

If you're snapping the gas open and the bike splutters a bit before clearing up and pulling, it's fuel height.  If it's clean but weak in the 4-6k range, then play with the needles and see what you think, they're pretty quick to change about.

[FJ-Doug]

While we're on the subject, I have a dumb question. If I'm to raise the clips on my needles from the 4th slot to the 3rd or 2nd slot from the top, will this cause my bike to run richer or leaner?   

Thanks,

Doug

[weymouth399]

lower the needle (by raising the clip) leans it out.
raise the needle (by lowering the clip) richens it up.
no dumb questions here
Bob

[FJ-Doug]

Thanks Bob... muchly appreciated. My '87 1200 has been running very rich (terrible fuel mileage and black, sooty plugs / exhaust. I raised my clips from the 4th to 3rd slot tonight but wasn't quite sure if I was making it worse or doing the right thing. I didn't get a chance to fire it up yet but hopefully all goes well.

Cheers!

Doug

[weymouth399]

Do you know who's jet kit is in it, and whats in it for jets.
should be between
PJ,37.5-42.5
MJ,110-120
AJ,145-165
Needle correct length some dyno kits the needle is about 3/16 shorter than stock that will richen her up.
Bob

[FJ-Doug]

Sorry for the late relpy...

The jet needles are stock (5FZ74) and I haven't gotten around to pulling the carbs to check the other jets. I'm assumming that since the needles are stock, then no aftermarket jet kit has been installed by previous owners.

I did raise the clip on the needle from the fourth slot to the 3rd (as specified in the manual) but it's far from running smooth like it did before. It was hard to start, took longer to warm up and idle is very rough (up and down).

I did notice that the mixture screws are 3 1/2 turns out so when I get a chance, I'll turn them in to 2 turns out like they're supposed to be to see if this helps. If not, I'll put the clips back to the 4th slot like they were and see how it goes from there.

The bike did run great before but a little on the rich side. I think part of my poor gas mileage was caused by a siezed front brake caliper as well. I friend from work tipped me off about this and I have since been able to free it up.

Hopefully all goes well and I can take it out for a long run to see if I can get more than 190 km's before I run out of gas.

Thanks again,

Doug