Mitsubishi works cam tuning

[shuggy]

Hi team.

After trial and error error error, I need some advice.

Imagine you have the following:

4g32 bored out 1.5mm
Standard pistons because the builders bored to much for the 1.0 flat tops
Beamed forged Rods and arp all round
Double valve springs
Number 5 original works cam
Twin down mikuni setup with custom high flow air box
Standard dizzy converted to electronic with standard springs and vac Chamber
4-1 extractors
2 inch exhaust with one muffler

Now.

Should valve clearance be standard? More? Less?
Should carby jets be stock or increased due to loss of vacuum from open air filter?
What static and max advance should be run? Do I need the dizzy recurved?

The reason I'm asking is I have it running and driving but it stumbles at high rpm and is gutless. It pings around 3 to 4 k rpm under light load and just doesn't feel right.

Carbys are fresh. Cam is good. Engine is good. All has done 1109km only.

Any help is amazing

[77GDWAGON]

I would try putting in a standard no 1 or 6 camshaft and see if you still get the pinging. I am guessing that with the 1.5os pistons and works cam u may be running lean at higher rpm. Works motors used the 4g32gs dizzy which had a static timing of 13` btdc and a different advance curve.

[75wagon]

I'm running pretty much all the same gear (without shared internal work to the motor), with the factory jets and I'm not having these problems.

I suspect your secondaries aren't working. If it's pinging at 3 to 4K it could be from running lean (what colour are your plugs?).
What spring is in your vacuum diaphragm for the vacuum secondaries. The spring from a single carb is too stiff.
Do you know for sure your secondaries open at all?

How does the carb set up work if you make the linkages work by hand (both the primaries and secondaries)? Does it rev out properly when you do that?

Dave...

[davetrees]

The solution is simple, really.

Take it to someone who knows what they are doing & get it tuned properly. (Doesn't need to be on a dyno, as long as they have a AFR sniffer).

Tuning a modified engine by trial and error is almost as useless as tuning via the internet.

[shuggy]

Thanks. I haven't got any money as just got back from a few months in Europe so pro tune out of the question. Might see if can find a mate with a wide band and a carby air flow thingy.

I will test the secondaries, I did think this actually, especially as with the Less Vacuum they would open at higher rpm anyway. I havea couple more sets so I will change the diaphragm. It's a brand new one so there is the chance it is a single spring. All jets wer gs spec though so I doubt it. I also have a manual conversion kit for the secondary so might install that?

Once I get money I will get it done right, but right now I just want it running!

[75wagon]

The reason I commented before about the secondaries is, my first set of twin carbs were incomplete. I fitted a vacuum diaphram off a single carb (it was missing off the twins) it din't work.
The twin carb secondaries vacuum spring is shorter and lighter. I assume it's because it feeds off the front carb, and there would be less vacuum off 1 of 2 carbs, then there would be off a single carb.
I've heard of a few people modifying the vacuum st up to mechanical, but i'm not seeing the point myself. If everything is working correctly, then they will come on when the motor needs them, any earlier is just using fuel for the sake of it IMO.

Take it to someone who knows what they are doing & get it tuned properly. (Doesn't need to be on a dyno, as long as they have a AFR sniffer).

I'm with you there davetrees, but tell me where you take one of these cars with twin carbs where they know what to do with it?
My experience is, carbs that aren't holleys or webers fit into the i don't know basket for most bokes that play with cars, and twins are even worse.
When I took mine originally to a carb specialist he scratched his head and said "H'mm, I've never played with these before, but I'll throw it on the dyno, and drill the jest out till it works. And that will be $100 an hour for dyno time, and twins usually take 4 hours. Oh, and I'll have to learn about these as I go".
Didn't really fill me with confidence

I ended up learning about them myself, and now I know and understand them, they work fine, and are so far maintenance free.

Dave...

[shuggy]

Quick one.

Will Weber DGAS jets fit?

I just fixed my 38/38 as it was running 0.2mm larger main jets on a 4g54. I bought heaps of different jets so might just start by giving up one size after I check the secondaries

Yeh when I took to get my carbs rebuilt they quoted 1k plus Coz they just didn't want to touch them

[75wagon]

Will Weber DGAS jets fit?

I wouldn't have a clue.

But I know this. The factory twins come with 1300 jetting. So if you change all three of the jets in the secondary circuit of each carb to 1600 jetting, that would fuel it up more.
Saying that though. I've never bothered changing the jets in mine, and they work fine.
If I were you, I'd just persist with making sure they work properly as they are, before I'd start fiddling with mods.

Dave...

[davetrees]

Will Weber DGAS jets fit?

No

[davetrees]

but tell me where you take one of these cars with twin carbs where they know what to do with it?

You find an old-school mechanic that grew up tuning carburettors. They exist, often in the back streets of industrial estates or in little suburban side streets, and they usually don't advertise on the internet ! You find them by word of mouth, often through car clubs & other enthusiasts.

The fact that they are twin carbs should be irrelevant, as is the make, pretty much, for someone who knows their stuff.

The factory twins come with 1300 jetting

No they don't. They are jetted to work with a 1600 with twin carbs. If they are the same jet sizes as used in a single carb 1300, that's co-incidence. If you put the jets used in a single carb 1600 into them, they will probably be rich as buggery.

If I were you, I'd just persist with making sure they work properly as they are, before I'd start fiddling with mods.

This ^^^

Make sure both carbs are working 100% properly. Have they been stripped & overhauled? Any air leaks ? You can't reasonably expect a set of old carbs to just bolt on & be fine.

Then adjust them so they are balanced properly, and opening exactly together, and the linkages are operating smoothly. The factory 4G32 workshop manual details the tuning/balancing process for twin carbs.

Get the tuning/balance right at idle, and on the primary circuit - that's where you spend most of your time when driving. Only then do you really need an AFR sniffer up the exhaust (either on the dyno, or on the road, which is how my rally car was done) so you can get the mixtures right at WOT and under load by changing jets in the secondaries.

[75wagon]

75wagon wrote:
The factory twins come with 1300 jetting
No they don't. They are jetted to work with a 1600 with twin carbs. If they are the same jet sizes as used in a single carb 1300, that's co-incidence. If you put the jets used in a single carb 1600 into them, they will probably be rich as buggery.

LOL, phrase it however you like, it all means the same thing. I am only quoting from what they actually did, not why.


Dave...

[77GDWAGON]

I still think u should try a stock camshaft. The no5 cam was designed for larger carbs than the factory down draughts. I think that daves no5 is a regrind and doesnt draw as much volume of air as an original no5 cam hence why his motor performs. I played around with many stock and reground cams and found the no6 gave me the best overall performance.

[shuggy]

Make sure both carbs are working 100% properly. Have they been stripped & overhauled? Any air leaks ? You can't reasonably expect a set of old carbs to just bolt on & be fine.

Carbs are brand spanking. All sweet.

Im going to try fiddle with a few things next week, thankyou for the effort in attempting to find an answer, i will let you know how i go.

I played around with many stock and reground cams and found the no6 gave me the best overall performance.

#6 is a number one suited for emissions am i wrong?


Anyway thankyou, i will let you know. Is it true that a Longer duration cam will cause less vacuum in the carb body? In this case i will just have to find a softer spring even moreso. Im going to:

Adjust valve clearance
Check plugs for running lean
Check ignition gap
Test secondaries with a camera
Try disconecting vac advance and winding timing right back
Try running a stock points dizzy
Try with different cam
in that order

Cheers!

[77GDWAGON]

#6 is a number one suited for emissions am i wrong?

it is the same as a no2 that's found in the 4g32gs motor, same valve timing and lobe heights.

[75wagon]

I think that daves no5 is a regrind and doesnt draw as much volume of air as an original no5 cam hence why his motor performs.

It's a stock cam that has been face welded, and ground to match the profile of a factory No.5. kodos got it done, and he had 5 of them done at the same time.

My carbs worked well with a stock cam, but the motor didn't want to rev past 5500rpm. With the No.5 it revs past 6000rpm, but the carbs hold the motor back after 6000rpm.
Nothing is my wagon is performance, everything has been just an add it as I get it type of thing (I know this is not ideal).
Nothing I have added has caused the car any problems in the way it runs. Sure it has changed characteristics of how the motor performs, but it has run properly through the rev range in all the different set ups/cams etc that I have run.

Stupid question: The cam is timed to the crank correctly isn't it?

Dave...

[davetrees]

#6 is a number one suited for emissions am i wrong?

#6 cam was the stock cam for GC/GD vintage Galants I think .... BUT it was also the stock cam in the Lancer 1600GSR (ie. the later-model 4G32GS engine) and therefore should be pretty well matched to a pair of twin downdraughts ... that's what the 1600GSR runs ex-factory. It's lift & duration is pretty close to the #2 cam (which is what the early Galant GS ran).

[shuggy]

Haha Yeh I hope it's timed right but probably worth checking! The shop installed it but may have not known how..

[davetrees]

When you say it "stumbles at high rpm" ..... what rpm are you talking ?

[mic_77]

What electronic dizzy set-up did you use for your conversion.

Cheers Mic

[Mitsiman]

Hi team.

After trial and error error error, I need some advice.

Imagine you have the following:

4g32 bored out 1.5mm
Standard pistons because the builders bored to much for the 1.0 flat tops
Beamed forged Rods and arp all round
Double valve springs
Number 5 original works cam
Twin down mikuni setup with custom high flow air box
Standard dizzy converted to electronic with standard springs and vac Chamber
4-1 extractors
2 inch exhaust with one muffler

Now.

Should valve clearance be standard? More? Less?
Should carby jets be stock or increased due to loss of vacuum from open air filter?
What static and max advance should be run? Do I need the dizzy recurved?

The reason I'm asking is I have it running and driving but it stumbles at high rpm and is gutless. It pings around 3 to 4 k rpm under light load and just doesn't feel right.

Carbys are fresh. Cam is good. Engine is good. All has done 1109km only.

Any help is amazing

You could have at any time contacted me via any method and I would have been happy to pass along some advice. There was no need for people to make the asusmption that we have built something wrong on the engine, or that we wern't prepared to help etc.

In answer to your issues, from what I can understand from what I have read

Should valve clearance be standard? More? Less? - valve clearances should be set to standard 6 and 10" clearance as per factory recommendations

Should carby jets be stock or increased due to loss of vacuum from open air filter? - Air filter will make no difference at all to the vacuum levels. That is purely a mechanical tuning / cam positioning / engine setup. What makes you think you have low vacuem?

What static and max advance should be run? Do I need the dizzy recurved? - should be running around 5 - 10 degrees at idle (Static, without vacuem advance) and around a total of 30 - 32 degrees (Without vacuum advance at WOT). In cruise modes vacuem advance should add around another 5 - 8 degrees in your cruise modes

The reason I'm asking is I have it running and driving but it stumbles at high rpm and is gutless. It pings around 3 to 4 k rpm under light load and just doesn't feel right. - quite clearly it needs tuning on both your fueling / timing. You could have issues with jet sizes, accelerator pumps etc. Just because you are using factory settings on jet sizes etc, it does not necessarily mean they are setup appropriator for your engine. The only way to solve it is to tune it properly, preferably on a dyno but you can do it on the road if you have the time, and equipment.

Thre is nothing wrong with the camsahft that has been fitted, nor has it been fitted incorrectly. I do not remember if you have had a vernier camshaft gear fitted, there is he ability to adjust it to move the power curve around for optimum results.

The electronic distributor would still need to be setup on the vehicle running Ie the base timing set with the vacuum advance removed once the engine was up and running. This can only be done once the engine is running. The distributor can be fitted at TDC but will be anywhere within 10 degrees of where it should be. I am assuming you have checked the timing with the car running? Tell me you didn't just start the car and drive it round with it set in the same position as it was when it left the workshop? If you have you could have it massivly over advanced which will cause flat spots, pinging and hard starting. This is the first thing that need to be checked.

Anyway that is where you need to start and work from there. Hope this all helps.

[shuggy]

Thanks mate. I have the timing at 10 degrees static at idle using a original dizzy with the guts of a Sigma electronic dizzy and module. It bounces all over the place at idle though so can't really say is exactly 10 degrees. Might try to find new dizzy guts and try that.

Im happy with the build. Except the oil in water from first use but I wanted to do a flush before I made any judgements if it was residue from the build as it's only a little. The engine has only just ticked over 1000km and have just done oil change and rocker adjustment. Still need to retourque the head if I need to do this at 1000?

Cam is not adjustable

Ive been driving my Wagon mostly as I've had overheating issues with this car ever since first drive but I think I've fixed it. Just need to fix the a/c pullet adjuster so it doesn't keep loosening and then good to go again.

[shuggy]

I will come and show the the car running in a couple of weeks.

I will have a stab at some things and use a wideband sensor to have A look. Then if I can't fix it I will give you money to do it for me

[Mitsiman]

No stress sounds like you are on the ball with it.

Whenever we do an engine build we use an acid cleaner on the inital clean and then it is flushed out with water and degreaser. There may be some residue degreaser in the engine block water galleries. That is why we always do a coolant flush on the 1st service at 1000km.

Definitly retorque the head at 1000km.

Look forward to seeing you when you come through

[shuggy]

Fixed two things today.

A. Worked out the secondary vac line doesn't provide enough vac so I moved the hose to the other side of the carby and now opens at wot.

B. The vac advance unit on the dizzy was advancing the dizzy 25 degrees on top of the mech advance. So I swapped the vac Chamber off another engine with a harder spring and all sweet

Just need to play around with timing now to get best performance.

Thanks for the tips!

[Mitsiman]

Excellent sounds like you are starting to get it really sorted out. Must be running a whole lot better now.

[shuggy]

a hell of a lot. But im going to need to find a softer vac chamber - using the other vac port on the carby isnt ideal.