1150cc piston kit, re jetting?

[Geert_Holland]

Good morning!

As you can see in my project topic I'm rebuilding my engine.
I needed new pistons and rings so I ordered a 1150cc piston kit.
I'm using a 6 into 6 exhaust and the original carburators and air filter.
Does someone know if I have to re jet my carburators?

All information about 1150cc mods are welcome.

Thanks!

[EMS]

Geert:

I am sure some of the carb gurus will be able to answer your question. For me, it is a tad too early. I am working on a set-up with 70mm bore pistons (yours are probably 68mm?) and a 6-6 for my 79 CBX., however, the head is being ported and flowed and the bike will be put on a dyno to determine optimal jetting. I expect it to be done by early next year. We can compare notes then, hopefully.

[Jeff Bennetts]

Geert, what is the elevation where you are at?

[Geert_Holland]

Hi Ems,
Thanks for replaying, yes my pistons are 68mm.
Your project sounds beautiful, could you post some pictures?
Always fun to see someone is doing like yourself, I'm expecesly
Interested in the head being ported, I'm thinking doing it myself.

Greets!

[Geert_Holland]

Hi Jeff, funny you ask, I never thought that would have impact on how the bike runs but it's offices it's does.
Holland is at sea level.

Thanks

[EMS]

Holland is at sea level.

Thanks

Or below

Geert:

No pictures yet. I don't do the porting and flowing. A friend of mine has a flow bench and he is an expert in porting and flowing. He has done several engines and built race bikes that his son is campaigning in AMA racing.
Only thing I can post is a picture of the 70mm cylinders and pistons...

[Jeff Bennetts]

So the things we know are,
1 You're using oversized 68mm pistons.

2 You're using a six into six exhaust.

3 the bike is going to live at sea level.

4 You're using the stock airbox, lid and filter.

My first question is what is the compression ratio of the pistons?

[Geert_Holland]

You are right Jeff, the only thing is I don't know the compression ratio.
I orded the 250 dollar piston set from eBay, heard some good story's about this set.

[Jeff Bennetts]

You are right Jeff, the only thing is I don't know the compression ratio.
I orded the 250 dollar piston set from eBay, heard some good story's about this set.

There is a thread somewhere here where those kits were mentioned, maybe some one here knows the ratio and will chime in.

Another question, what coils and ignition are you using?

[Geert_Holland]

That would be great.

I'm using the original coils and ignition.

[EMS]

Compression ratio: Using the definiton of compression ratio, one can estimate closely what the new one will be. If the displacement increases from 1047 to 1150 = 103cc = 9.83%, so will the compression ratio. From 9.3:1 to 10.2:1

[Jeff Bennetts]

That would be great.

I'm using the original coils and ignition.

Since the bike is apart check the ignition components, make sure the 3 pickups are clean, the springs are on the advancer weights and that everything moves freely. There is no oil sitting at the bottom of the ignition housing or dripping from the ignition lead wire grommet, if so replace the seal in the back of the housing/clutch cover and the O ring on the ignition shaft, look at the shear pin too, make sure it's not bent.

Check all the connectors on the wiring harness for corrosion and clean them up, check for signs of over heating, replace them.

After you get it running, make sure your charging system is working properly.

Check the voltage output of the battery, then check the input to the coils, a 1V drop is almost a 10 % loss. There is a thread on here about the relay mod that bypasses the harness and sends the voltage straight to the coils.

Well I sent this thread sideways but you need a good spark if those pistons are a higher compression ratio than the stock 9.3 to 1

Carbs

Main jet, secondary 110 to 120 range
Main jet, primary....80 +/-2

Why don't you skip the shimming of the needles for now, that can be done on the bike later if you want to. Do the accel pump adjustment instead.

Shim the spring 2mm
Set the pump diaphragm actuating linkage tab to Ø lash
Bend the bottom of the limiting tab towards the top tab a bit to increase the accel pumps duration.
Make sure the accel pump diaphragm is fresh, no pin holes and still pliable, or just buy a new one. Confirm the pump is working by holding the carb bottom with the pump diaphragm installed and some gas in the bowl, pump the shaft and watch for a good strong spray, wear eye protection.

Put the bowl on the carb bank full of fuel and actuate the throttle linkage on the bench and make sure all the brass nozzles in each carb throat has a strong steady stream, you can also check your accel pump adjustments now before you install the carb bank back on the bike.

Seat the mixture screws gently and back them off(open) 2 1/4 turns.

Sync the carbs on the bike but you will need to sync them again after the motor is broke in(valves seated) and the carbs are set the way you want them just to verify everything right.

Hopefully Dave will show up and give his thoughts on all this and you will be good to go.

[EMS]

Good advice! darn, I need to find that "relay mod" post. Don't even remember that!

[Jeff Bennetts]

Good advice! darn, I need to find that "relay mod" post. Don't even remember that!

I'm thinking falldownphill started it or joined the thread with the mod or maybe it was Kool Biker, I need Pope to remember this for me.

[daves79x]

Good stuff, Jeff. Re the carbs: Need to verify what model they are first. This is an '82 engine, so they might be late model. Check the number - VB60 or 61 are early carbs, VB62 are '80 only, and VB63 or 64 are late model. Jeff's recommendations apply only to the early carbs. However, with the stock intake, I think you leave the main jet alone. Work on low and mid-range, but first we need to know what carbs we have.

Dave