some jetting help

[bigb9582]

here soon im gonna replace the rusted pipes on my 79f. not haveing the money for a new exhaust system, im gonna put on glasspack mufflers like the ones you would put on a car.

these mufflers are a strait through flow. i read the jetting howto and it says----1 size up for a custom 4-2 exhaust and 2 sizes up for open headers/no mufflers.

what would these glasspacks be considered?? they are a strait flow but are mufflers.

has anyone ever put these on a bike?? i am looking for a good bit of sound but not open headers/strait pipe sound.

btw i searched with no luck.

[Dennyz]

Car glass pack mufflers have been done before. The biggest draw back is their weight. The upside is they last forever. I would stick with the stock jetting and see how it goes.

[Tusler]

Jet size help

I recently put individual filters on my carbs and had a jetting question.
A forum member posted this and it helped me figure what size I needed.
Hope it helps-

http://www.xs11.com/forum/showthread...=&threadid=382

[bigb9582]

Re: Jet size help

Originally posted by Tusler
I recently put individual filters on my carbs and had a jetting question.
A forum member posted this and it helped me figure what size I needed.
Hope it helps-

http://www.xs11.com/forum/showthread...=&threadid=382

yeah i read that. but thats were i got confused. i didnt know if they would be like straight pipes/no mufflers because of their strait threw flow taking 2 jet sizes up or just another custom 4-2 exhaust only taking 1 size up.


dennyz- you realy think stock jetting would be ok?? i figured since they were straight flow it would cause some jetting problems.

[TopCatGr58]

Hey BigB,

These bikes can run fairly decently on leaner mixes, and you get better mileage. Before I knew better, I put a 4-1 pipe on mine replacing the OEM's, and didn't rejet for 9 years, had power up to redline, ran several long distance runs...over thousand miles, never burned up any pistons!!!

Keep a close eye on your plugs, and monitor your engine response, listening for Pinging/knocking.
T.C.

[Dennyz]

Although your glass packs are straight through, they still represent back pressure to the air flow.

The reason I suggest running with stock jetting is to establish a reference. Jetting is a relative thing. It all depends on the individual motor and what the rider want to accomplish (or feel).

You won't hurt the motor. You may experience a flat spot in your throttle response somewhere in your driving RPM range. Or, it may just run fine. Regardless, you will have a better idea what steps to take in jetting, if any.

[GARTHXS]

yeah what he said

I just installed 4/1 pipes and pod filters and it takes mucho patience and trial and error to rejet correctly after a couple of tries you will get it there is no magic ## when it comes to jetting because everone seems to have there own ideas on what is the better setup, some say you will lose bottom end with a 4/1 but mine pulls so hard I have to hang on real tight when I go WOT

[bigb9582]

cool thanx for the replys guys. ill probly order the next size up jets just to have them in case when i do the exhaust.

[Dennyz]

My current thinking is to increase the pilot jets first. I am finding that by keeping the pilot jet on the larger size (45.0), I can reduce the main jet (142.5 - down from 145.0) and improve my mileage without the loss of the seat of the pants performance (torque) the XS is famous for (on '78-'79 carbs). I am toying with the idea of dropping my mains to 140.0 to see how the power feels and what happens to the mileage.

I am basing this on what happened when I dropped the pilots to stock (42.5) and set the mains to 142.5 in an attempt to improve mileage. The low end power went away and made the motor sluggish and unexciting. My mileage showed no significant change. I put the 45.0 pilots back in and the low end improvement was instantly noticeable. My mileage went from 32-35mpg, to 35-38.

A good friend and fellow XS'er has Dyno data that suggests that the stock main jets can support typical intake and exhaust modification. I believe that most of what we do to the intake and exhaust impacts the low end the most. Basically causing a significant lean out under 2000 rpm. This is the realm of the pilot jets on the first generation carbs.

It is my impression that on second generation carbs, the pilot circuit draws from the main jet stream. This makes jetting more interactive and more elusive.

That's my $0.02

[bigb9582]

so u think i should go up one on my pilots before i do the mains??
thats is a interesting point bout the low end performance.

[Dennyz]

I suggest doing no jetting first and change the pilots if you need to.

[DavesXS]

Many find the stock pilot size is plenty. I bumped mine up one size but havn't colortuned yet. I ordered a few sizes from MikesXS at $6 a pair.

[bigb9582]

Originally posted by Dennyz
I suggest doing no jetting first and change the pilots if you need to.

cool thanx. when i get to it here in a couple weeks ill let everyone know how it goes.