Topic: '78 CB750k conversion to cafe racer (yes, more issues)

[deafcaferacer]

You can leave the IMS at 1/2 a turn if it runs better... sounds like it could still be better though. The jet you were testing with this test was the idle jet. For a custom setup (air box mods, pods, stacks, etc) usually you change idle jet sizes until your optimum setting is 1 turn out +/- 1/2 a turn. I believe outside of these ranges the metering of fuel/air starts to change drastically.

To test if you need a larger main jet you'll need to do some plug chops at WOT.

IW

Read my mind..was going to do plug chops next. No place round here to go WOT but I've read that it serves the same purpose to come in just under redline in 2nd.

[iron_worker]

It doesn't need to be at redline. What is important is the throttle position. To get a true picture of what's going on at WOT (main jet) you need to be at WOT (Wide Open Throttle). You need to be somewhere where you can hold it at WOT for long enough to get the plugs to be able to build up a residue. So, in this case a long straight hill really helps to keep the speed down.

IW

[deafcaferacer]

Well I went WOT for as long as I could on the nearest hill I could find and went through the chop procedure and the sparks show very lean as far as I could tell- no residue and no brown color.

So I guess move up to 120 main (from 115 which is what is on there now)? Does there also need to be a corresponding change for slows? Or can it stay the same?

[deafcaferacer]

Bump.. would appreciate some feedback please.

[harisuluv]

so you have pods and you didn't change your needle height?  pretty standard if you want to run pods, you raise your needles and then go up on the main jet. 

Since you have a 78, this has no adjustment clips, so you would have to use shims.  You could probably go to a 105 or 110 main jet.

It usually isn't necessary to change the idle jet.

[SOHC4 Cafe Racer Fan]

I had to do the same with my carburetors on my 550 when I went to pods.

[deafcaferacer]

I actually have '73 carbs so I should be able to raise my needles another notch.

Finally got a day off so I can take the carbs off and do this, at last.

Is there any way to unscrew the needle from it's position inside the slider cylinder without messing around with the slide adjuster screws? I am dreading the possibility of messing up the carb syncs.

[flybox1]

Is there any way to unscrew the needle from it's position inside the slider cylinder without messing around with the slide adjuster screws? I am dreading the possibility of messing up the carb syncs.

As soon as you touch those slides, you're going to need to bench and vac sync again 

[deafcaferacer]

Ugh..

Will have to save up to get a vac sync.

Still a little flat towards the upper range, and a slight lag on sudden acceleration- can live with that for now.

Thanks anyway.

[deafcaferacer]

Did WOT then chops as best as I could on a small hill near me- considering I live in an intense populated area.

Light gray look- which is normal, right? Or maybe I did not WOT enough to build up a residue...

[flybox1]

If my chop was as good as I could do....i'd say thats a bit lean still, and IIWM, i'd go up by a 5.
(ie. 120 ->125)

pics are good here...
http://www.turbododge.com/forums/f4/f62/624186-reading-spark-plugs-troubleshooting-guide.html

[deafcaferacer]

If my chop was as good as I could do....i'd say thats a bit lean still, and IIWM, i'd go up by a 5.
(ie. 120 ->125)

Could I do that over raising the needles? I have 115 so I'd go up to 120.

Not sure what the benefits are for raising needles vs. going with bigger mains.

[flybox1]

needles are mid-range....leave them where they are.
up your mains to 120, and then do another plug chop, should be really close.
once you're satisfied, do a mid range plug chop (1/2 - 2/3rds throttle position) to determine if your needles are in the right spot to give you the correct mixture.

[deafcaferacer]

Thanks, Rob.

Have ordered 120 mains. Sitting tight until they arrive.

Going to go back to reading everyone else's builds in the meantime.

[deafcaferacer]

Question, could I swap the main jets with the carbs still on the bike?

Or do I have to pull the carbs to change the jets?

[flybox1]

Question, could I swap the main jets with the carbs still on the bike?

Or do I have to pull the carbs to change the jets?

you dont have to pull them, but if you have big hands like me, getting the bowl screws out sucks.
its faster for me to take the carbs off.

[deafcaferacer]

Question, could I swap the main jets with the carbs still on the bike?

Or do I have to pull the carbs to change the jets?

you dont have to pull them, but if you have big hands like me, getting the bowl screws out sucks.
its faster for me to take the carbs off.

I do have big fat hands, but fortunately the bowls are clip ons. 

Had a window today to put in the new jets before it started to rain again and took her out for a ride, she kicks like a mule now and I have power in the upper range now.

Tried to do a WOT, but did it improperly. I think I know another place to do it to get much closer to the 2-3 minutes of WOT necessary to get an accurate read. Will report on this when I can get another ride in.. raining now and more rain tomorrow, but Sunday will be perfect.

[flybox1]

Had a window today to put in the new jets before it started to rain again and took her out for a ride, she kicks like a mule now and I have power in the upper range now.

[deafcaferacer]

I just noticed that the rear brake isn't engaging very well and that the rear brake pedal doesn't spring back firmly.

I suppose this warrants a look inside the rear brake cylinder? Feels like a worn spring at work here.

[flybox1]

Disconnect the long footbrake connecting rod(spring and adjustment screw) from the drum brake lever.  Actuate both the foot lever and the drum lever manually and you'll be able to tell where to focus.

[iron_worker]

Are you using fresh plugs for your chops? Doesn't look like it.

IW

[deafcaferacer]

Disconnect the long footbrake connecting rod(spring and adjustment screw) from the drum brake lever.  Actuate both the foot lever and the drum lever manually and you'll be able to tell where to focus.

I did this and could not find anything wrong at either end.

But what I noticed was that when I activated the drum level with the tire off the ground, it stopped easily enough.

But when riding the bike, and testing the rear brake by using it isolated, it doesn't brake good. Could the shoes be worn out?

[deafcaferacer]

Are you using fresh plugs for your chops? Doesn't look like it.

IW

No, I'm not. I suppose I should get some new plugs?

[flybox1]

But when riding the bike, and testing the rear brake by using it isolated, it doesn't brake good. Could the shoes be worn out?

possibly, but you'll want to pull the drum apart and check.
if you've got good meat on your pads, you can put some emery paper to the ID of the drum to deglaze it a bit, and dry rag wipe all the brake dust (dust mask suggested - asbestos maybe) and clean it up.  Blow out(outside) with air if you have it.
Re-assemble, and give the brake lever adjuster spring nob a turn in, or three, from its last position to allow the pads to engage earlier in the brake lever travel.

[deafcaferacer]

But when riding the bike, and testing the rear brake by using it isolated, it doesn't brake good. Could the shoes be worn out?

possibly, but you'll want to pull the drum apart and check.
if you've got good meat on your pads, you can put some emery paper to the ID of the drum to deglaze it a bit, and dry rag wipe all the brake dust (dust mask suggested - asbestos maybe) and clean it up.  Blow out(outside) with air if you have it.
Re-assemble, and give the brake lever adjuster spring nob a turn in, or three, from its last position to allow the pads to engage earlier in the brake lever travel.

Thanks for the tips. Will do this tomorrow and report back.