School me in the ways of intaking fuel and air...

Well,

That sucked...

Long story short...

Tried to tune, not much luck, Dan Sprongle came over at 6:00 pm Friday to give us a hand. We didn't have time to find jets, but we tried everything else. I dropped the needles all the way (earlier) we rand 30 degrees and more of advance, tried shutting down the fuel pump to cut pressure, ran colder plugs, pulled the air box off, yadda yadda yadda.

The car made great power potential under 1/3 throttle, so there's hope, but it was too hard to drive when the diff between idling, running and bogging was about 1/8 inch of pedal throw...

So at 8:00 pm we made the decision to swap back to the stock carb (which we knew wasn't working well either...). Unfortunately that involves swapping the head... So at 1:00 am after a trouble shooting many problems on the stock carb, we had a running rally car.

We started the car in the morning and it ran like $h!t... but we'd already paid our money and thought, lets go out and see what happens, maybe at first service we can get it better...

First stage was so down on power I didn't think we'd make slow time! We stopped on transit and debated going to 2nd stage. Decided screw it, we'll go back to service. I fired the car back up and suddenly it ran well! Okay we're 15 minutes late, but lets go!

By the time we got to teh second stage it was running poorly again. We got passed twice on A2!!!! I've never been passed before, that was sad.

Pulled up to the finish of A2, pushed in the clutch and BANG the cable snapped. WTF.

Limped back to service cut the cable housing in half, tried to link the cables together, left service with barely time to make the start of A3 (should have thrown in the towel...). But on transit the clutch was slipping from the poor rig. I stopped to adjust and the with a minute or 2 the 000 car came up and shut us down.

Moral,

More prep, more time, and more tuning needed.

Good news:

I only need the brakes twice, both on downhill sections in A2, but the big brakes swap and the braided lines are awesome!

Even my rigged suspension is working "good 'nuff" for now. The car feels way better and more solid with all the shell work and stiffening.

So now I need to build a motor that works.

Next year.

Do you have a wide band o2 sensor, or at least a sensor bung in your exhaust? That would make tuning much much easier. You would then actually know the AFR without having to make guesses.
Another thing about motorcycle carbs that everyone assumes: They're simple.
I think that is completely false. You have main jets and idle jets, idle mixture screws, needles (position and profile), emulsion tubes that vary, with CV carbs you also have to deal with spring pressure.

We built and tuned a quad carb manifold for a pinto powered circle track car. After a full day of tuning (no wide band) it was running "pretty good". It took a few more races to get it dialed in right. This was with much more simple Mikuni round slides w/o accelerator pumps. We've also built and tuned a number of setups for honda 4 motorcycles that used two larger carbs instead of four. Drastically increased lower end tuning(below 6k).

Also, what year of bike did those carbs come off? If it was anything late 80s to mid 90s they were probably so lean from the factory that the bike barely ran when new. We just jumped 4 main jet sizes on a 600 yamaha 4 last weekend. Went from not running past 4K on the freeway to running like a rapped ape in any gear. So maybe your actually lean and not rich?

Yeah,

A wideband was planned, but never acquired...

Too much in too little time. Some may say I should have stuck with the stock carb for this rally, but it has issues too, and we didn't know that until last weekend, when the car was finally together enough to run it on the road. The thing is an incredibly complicated computer controlled Hitachi thing. I better understood the basics of the mikunis and thought we could tune them in time.

Basically real world stuff got in the way, and I couldn't take the week off!

So yep,

To tune next:

Wide band
A bunch of jets
A nice gravel road in the summer
A nice lunch packed
No stress

Make it go.

Oh yeah, and I agree... carbs are not simple! For a moment on the way home, I thought hmmm could use the carbs as throttles, and run megasquirt...

But getting the carbs working will work, it will just take time.



Edited 1 time(s). Last edit at 11/28/2011 11:45AM by Mad Matt F.

Quote
Robert Culbertson
Do you have a wide band o2 sensor, or at least a sensor bung in your exhaust? That would make tuning much much easier. You would then actually know the AFR without having to make guesses.
Another thing about motorcycle carbs that everyone assumes: They're simple.
I think that is completely false. You have main jets and idle jets, idle mixture screws, needles (position and profile), emulsion tubes that vary, with CV carbs you also have to deal with spring pressure.

We built and tuned a quad carb manifold for a pinto powered circle track car. After a full day of tuning (no wide band) it was running "pretty good". It took a few more races to get it dialed in right. This was with much more simple Mikuni round slides w/o accelerator pumps. We've also built and tuned a number of setups for honda 4 motorcycles that used two larger carbs instead of four. Drastically increased lower end tuning(below 6k).

Also, what year of bike did those carbs come off? If it was anything late 80s to mid 90s they were probably so lean from the factory that the bike barely ran when new. We just jumped 4 main jet sizes on a 600 yamaha 4 last weekend. Went from not running past 4K on the freeway to running like a rapped ape in any gear. So maybe your actually lean and not rich?

Er er uh..
Matt you listening?

---

John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.

Yeah listening...

But um, the carbon soaked plugs, and the dripping fuel from the leaking exhaust (maybe a bit of exaggeration) , and fuel vapour cloud in the air behind the carbs... I'd still say rich.

However...

Wideband tuning is the plan (was the plan, but no time to get it set up).

Now I just have to lick my wounds (literally, my hands look like greasy hamburger, and they ain't no keyboard queens to start with!) and plan a few other things.

The motors are notorious for ripping through lower end bearings, and while we maintained oil pressure above 10 pounds... it still fell. Most people blame the bearings, but those of us that have changed more then one set, blame the pump.

I'm thinking I need to up to an external oil pump or something too.

The simple Justy gets complicated.

I otter buy a volvo.

Matt

One thing to consider to is a airbox that can act as a plenum at wide open throttle, and maybe add some balance tubes to the runners. With multi-carb setups, it is very important to have the carbs synchronized ("sync'd" to each other. By having all cylinders running exactly the same you get better response and tuning. This is done by having them open different amounts initially. You can use a vacuum gage ($100 for a 4 cyclinder set up) or use ball bearings and have them drop through the carbs at the same time. The latter option has them all opening the same amount, assuming everything is equal. With the gage you can tune each carb to the cylinder.
Also, stick with the flat slides that you have. They are probably one of the best carbs ever made. Simple (for a carb) and very easy to tune (relaltively), and you won't need to go any bigger than 33 or 34mm. Our Honda CRF450 (water cooled 4-valve head) with a 40mm carb produced 54hp and ran the entire season w/o rebuild. The TT500 (540cc) Yamaha (air cooled 2-valve head) was @ 46hp with a 38mm carb. Now imagine a justy with 110+hp: the right cam, ported head, good valve seats, higher comp, possible larger valves (definitely lightened SS ones)...

Matt, your testing plan seems pretty solid. Also try and find a big hill, something you can do full throttle pulls on. Keep a log of carb settings and times up the hill (have markers and a standard entry speed and gear). This will help eliminate the "seat of the pants" tuning. We use a big paved hill to tune our dirt track bikes on, works better than a flat gravel road because you can actually load the engines.

Alright, I'm going back to try and pass some classes.

Quote
Robert Culbertson
One thing to consider to is a airbox that can act as a plenum at wide open throttle, and maybe add some balance tubes to the runners. With multi-carb setups, it is very important to have the carbs synchronized ("sync'd" to each other. By having all cylinders running exactly the same you get better response and tuning. This is done by having them open different amounts initially. You can use a vacuum gage ($100 for a 4 cyclinder set up) or use ball bearings and have them drop through the carbs at the same time. The latter option has them all opening the same amount, assuming everything is equal. With the gage you can tune each carb to the cylinder.
Also, stick with the flat slides that you have. They are probably one of the best carbs ever made. Simple (for a carb) and very easy to tune (relaltively), and you won't need to go any bigger than 33 or 34mm. Our Honda CRF450 (water cooled 4-valve head) with a 40mm carb produced 54hp and ran the entire season w/o rebuild. The TT500 (540cc) Yamaha (air cooled 2-valve head) was @ 46hp with a 38mm carb. Now imagine a justy with 110+hp: the right cam, ported head, good valve seats, higher comp, possible larger valves (definitely lightened SS ones)...

Matt, your testing plan seems pretty solid. Also try and find a big hill, something you can do full throttle pulls on. Keep a log of carb settings and times up the hill (have markers and a standard entry speed and gear). This will help eliminate the "seat of the pants" tuning. We use a big paved hill to tune our dirt track bikes on, works better than a flat gravel road because you can actually load the engines.

Alright, I'm going back to try and pass some classes.

Excellent advise.
Note however a "damn good" job on sync can be done using the precision devices that we base micrometers on: threads.
Count threads.
half turn is a half turn is a half turn.
Requires looking real hard at the thing and making accurate turns.

Matt, that firebreathin thing an aluminum block?
You doubless know exactly the oil temp you're running, so we'll ass-sume the oil temp is under control.
Cause I've heard of alloy block things loosing pressure when the block grows.

So is it aluminum?

---

John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.

Al-oo-min-ee-um???? Buwaa ha ha ha ha Bu ha ha Waaaa Haaa haha hahh..

No silly, cast from a recycled war boat anchor!

Ah it's like the list of "shoulda woulda"s... yeah, planned for an oil cooler, didn't get it made up. Need a sandwich adapter or.... my thoughts of external plumbed pump...


Yeah I thought about adding balance tubes between the runners... I did bench sync the carbs to open at the same time. But not under actual wa-cu-um. I have an MG... that at one point had SU's (before I owned it...) and do have a sycn gauge thingy. I didn't have time to find the box it was in...

I should post a pic of the airbox, it was classic! I made a box out of tin in about 10 minutes, cut some holes in it, sealed it with tape and stuck an inlet hose we had lying around in the side of it... the R&D department was um... lacking.

For an oil cooler, check Jegs: they have an adapter plate with a bunch of different threaded adapters (silimeters and the superior inch). I think it was $60 with 10' of tubing and the fittings.
If you can keep an MG running, you can get this thing to run correctly!
I've also made some pretty "innovated" parts when the the time was running out. Catch cans out of 32oz beer cans work great, and you can mount them with zipties and velcro!

Quote

If you can keep an MG running, you can get this thing to run correctly!

Ha, it's easy! However keeping the lights on....

Quote
Mad Matt F

Quote

If you can keep an MG running, you can get this thing to run correctly!

Ha, it's easy! However keeping the lights on....

I had a Jaguar XJ6 when I was in high school, the only electrical problem it ever had was the fan relay going out. My BSA 250 on the other hand is a nightmare of electrical problems. I have been going through and replacing all the Lucas bits with updated steady state stuff and electronic ignition. First kick starting and bright lights for the win!

Quote
john vanlandingham
Note however a "damn good" job on sync can be done using the precision devices that we base micrometers on: threads.
Count threads.
half turn is a half turn is a half turn.
Requires looking real hard at the thing and making accurate turns.

Even more better, for only slightly more (slighty more than free, is still not a lot ), can be done with a length of garden hose. Chop off about a foot or so, so you can insert the end into the runner while the engine is idleing, holding the other end to your ear. The sound changes depending on the amount of opening. Get all runners to sound equally.

With a bit of practice this is both pretty precise, and fairly quick. I used to be able to do it in about 15 minutes including removing filters and refitting when doing it on my 4 banger Opel many moons ago.
I picked up this black art again a few years ago when my Golf was running ITB's. It was a set of Toyota ones - 4 individual, so a lot of fiddling to synchronize 4 individual runners as opposed to 2 doubles (Weber DCOE's on my Opel and later Escort).
Incidentally a friend of mine had one of those tools that measures the synchronization, so just for shit and giggles, we measured just after having done one of my "synchronize-by-garden-hose"-sessions, and it turned out that I was just about spot on by doing it by ear...

---

Brgrds
Brian

Quote
wildert

Quote
john vanlandingham
Note however a "damn good" job on sync can be done using the precision devices that we base micrometers on: threads.
Count threads.
half turn is a half turn is a half turn.
Requires looking real hard at the thing and making accurate turns.

Even more better, for only slightly more (slighty more than free, is still not a lot ), can be done with a length of garden hose. Chop off about a foot or so, so you can insert the end into the runner while the engine is idleing, holding the other end to your ear. The sound changes depending on the amount of opening. Get all runners to sound equally.

With a bit of practice this is both pretty precise, and fairly quick. I used to be able to do it in about 15 minutes including removing filters and refitting when doing it on my 4 banger Opel many moons ago.
I picked up this black art again a few years ago when my Golf was running ITB's. It was a set of Toyota ones - 4 individual, so a lot of fiddling to synchronize 4 individual runners as opposed to 2 doubles (Weber DCOE's on my Opel and later Escort).
Incidentally a friend of mine had one of those tools that measures the synchronization, so just for shit and giggles, we measured just after having done one of my "synchronize-by-garden-hose"-sessions, and it turned out that I was just about spot on by doing it by ear...

Haha, that's awesome.

Quote
Dazed_Driver

Quote
wildert

Quote
john vanlandingham
Note however a "damn good" job on sync can be done using the precision devices that we base micrometers on: threads.
Count threads.
half turn is a half turn is a half turn.
Requires looking real hard at the thing and making accurate turns.

Even more better, for only slightly more (slighty more than free, is still not a lot ), can be done with a length of garden hose. Chop off about a foot or so, so you can insert the end into the runner while the engine is idleing, holding the other end to your ear. The sound changes depending on the amount of opening. Get all runners to sound equally.

With a bit of practice this is both pretty precise, and fairly quick. I used to be able to do it in about 15 minutes including removing filters and refitting when doing it on my 4 banger Opel many moons ago.
I picked up this black art again a few years ago when my Golf was running ITB's. It was a set of Toyota ones - 4 individual, so a lot of fiddling to synchronize 4 individual runners as opposed to 2 doubles (Weber DCOE's on my Opel and later Escort).
Incidentally a friend of mine had one of those tools that measures the synchronization, so just for shit and giggles, we measured just after having done one of my "synchronize-by-garden-hose"-sessions, and it turned out that I was just about spot on by doing it by ear...

Haha, that's awesome.

No, Its standard practice sine the 1920s. Every British carb tuning manual, every Weber tuning manual since forever will have pictures of using a bit of hose as a "hearing aid".

But first, before anything the carbs must start from a base position.

---

John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.

Oof! This thread is reafirming my love of mid 80's Bosch fuel injections stuff from the junkyard. It plugs together like lego, and always goes!


Best of luck there Matt. I like the "bring a lunch" part of your tuning protocol.