Jetting recommendations

[krakum1967]

I am almost done with my rebuild of my 78 XS1100E, and have some questions on jetting. The bike will have two 2 into 1 K&N Filters, and came with an abscure set of Kerker pipes. They "Bell" out and are dfintely not stockas they have no crossover.

At any rate, the pipes are pretty open, and I the K&N's will give it a lot more air. Past experience says to rejet, one step for the exhaust on the main, one for the change in air intake, and one on the pilot jet.

If memory serves me correctly, that would be 142.5 mains (being stocks are the 137.5) and I will have to check the pilot as I cannot remember.

Will this be too rich? I know ultimately it will be reading plugs and possibly a Dyno run, but just looking for pointers.

Thanks in advance

[TADracer]

IMHO, before you make any changes to jetting, make sure everything else is in order (ign. timing, vacuum advance mechanism, centrifugal advance mechanism, valve clearance, cam chain tension, etc.) and then try the stock jetting with fresh spark plugs in the stock heat range. Read your plugs and go from there. If you make a jetting change 'just because' you have exhaust and intake mods you might be setting yourself up for a bit of tail chasing which happens all too often.

If you need jetting changes, I recommend you tune the carbs from the top down. www.factorypro.com/tech/carbtun.html

[DGXSER]

I agree with TAD. I recently completed an SG project that had POD filters with Kerker 4-1. I thought sure I would need bigger jets. But..the PODs had stacks on them and the Kerker had a brand new baffle and packing. With this, it ran great on 112 mains with 42.5 pilots, and stock air jets. So do start with stock and see where you need to go. One of the reason's the PO sold the SG was he could never get I tuned right. What I found was it had huge mains in it 145 IIRC, 45 pilot jets, and it was running rich, so he had dropped the floats to about 27 mm. This was on 80-81 model carbs. So it was jetted up huge and then leaned by the float heights.

BTW, I have a bike that has a 4-2 system on it that has a Kerker sticker placed on it. It has been discussed here before, I do not believe Kerker ever made a 4-2 system (assuming you meant a 4-2 when you stated 2-1).

The UK version of our site has a great set of pictorials to help figure out the exhaust you might have on your bike.

[trbig]

Most suggestions I've seen say to not change the pilot jet unless you go at least three sizes up on the main. 137.5 is already a huge main jet, so I'd run it as-is and do some plug checks and maybe some checks with a heat gun on the exhaust if possible.

[krakum1967]

Motor is fresh top end, I have new pistons, cylindr, rings, head was gone through, valve clearance is fine and set, ports are cleaned and the head was dipped, new valve seals and springs...yada yada yada, like I said, I am at the stage of carburator rebuild, I agree the stock jets are huge, so I will stay stock, and rebuild the carbs from there, at least I can tear down first and check it out.

[TADracer]

Yep, 137.5's are the stock size main jets for a 78E and 42.5 for the pilots.