Engine Tuning Any Gurus??

[springersrolla]

gday i have a brand spankin rebuilt 3k with a rebuilt standard 3k carb with 5k primary and secondary jets freshly kitted, little cam and a full 2" with extractors, anyways its been running high on idle, and ive just had the exhaust done so i want to tune the motor properly. I have a dodgy monsta tacho thats reading 1800-2000rpm at idle but it sounds round1300-1500 i've set the timing with timing light around 10-12degrees, but when i go to drop the idle of the motor down under a1000 it runs for around 10secs and then drops revs and wants to die, i need the car to hold a steady idle but i don't think it needs to be at over 1000. anyone out there with a few tricks or something i should be looking out for, like slip or incorrect alignment of the notch on the harmonic balancer or could it be a carby,float level, dodgy dizzy or jetting problem??? anyone with any advice would be great, but if someones handy with the k motors with the right tuning tools and wants some cash to look at it, or can recommend a good gas analysier/tuning shop for shitty little carbs would be good, i can travel anywhere round brizzy, i just want the car sorted so it can be run in properly and driven to be enjoyed not running high on idle.cheers for the read

[Jimpoole]

Ok since no one has posted I wil add my 2 bob.

I'm no guru, In fact I'm only 18y.o, but doesn't it seem a little odd to you that are putting jets that are meant to run on a 1500cc on a 1200cc?

Set your timing to 8 degrees. No point buggerising around with advanced timing if your engine doesn't even idle. It'll ping under load with timing like that anyway. Keep that for later.

Get a cheap engine analyser and set the idle speed to exactly 750rpm. Or if you can't do that, just guess a speed. You're usually within 50-100rpm anyway.

You quoted "shitty little carbs". Mate, they mightn't be the best carbs around but they do the job, until fools decide to put oversized jets in them. Just leave it how it is.

Anyway, I hope the rebuilt 3k goes well for you. It all seems good, apart from the oversized jets. Just put the standard ones back in, and it should be sorted.

If you need more power, the only way to do it is to get a bigger carb. A few suggestions are 32/36 Webers (usually off Escorts) which do need downjetting, and Nikki's off Izuzu Gemini's.

[Raven]

Ok since no one has posted I wil add my 2 bob.

I'm no guru, In fact I'm only 18y.o, but doesn't it seem a little odd to you that are putting jets that are meant to run on a 1500cc on a 1200cc?

Set your timing to 8 degrees. No point buggerising around with advanced timing if your engine doesn't even idle. It'll ping under load with timing like that anyway. Keep that for later.

Get a cheap engine analyser and set the idle speed to exactly 750rpm. Or if you can't do that, just guess a speed. You're usually within 50-100rpm anyway.

You quoted "shitty little carbs". Mate, they mightn't be the best carbs around but they do the job, until fools decide to put oversized jets in them. Just leave it how it is.

Anyway, I hope the rebuilt 3k goes well for you. It all seems good, apart from the oversized jets. Just put the standard ones back in, and it should be sorted.

If you need more power, the only way to do it is to get a bigger carb. A few suggestions are 32/36 Webers (usually off Escorts) which do need downjetting, and Nikki's off Izuzu Gemini's.

 

The reason he's put the bigger jets in is because the engine has been rebuilt with a different cam grind. :wink:

[Jimpoole]

The reason he's put the bigger jets in is because the engine has been rebuilt with a different cam grind. :wink:

Yeah I know that, but still isn't it the case? Won't run on oversized jets. Still better off with a larger carby.

[Felix]

does that carb have a fuel cutoff solenoid? If so is it working properly?

 

Some of the real early carbs have a blank off bolt that goes in where the cutoff solenoid is on the later carbs. Removal of the cutoff solenoid makes the stock carbs way more reliable.

 

Might not be your problem, but it is pretty basic to check.

[springersrolla]

ok so thanks for the response jimpoole but the jets are fine in the car it does NOT ping at all through the rev range, and yes it does still idle, just high, theres no point in me trying to even retard the timing to 8 because it'll just die,or run at like 2000rpm to hold 8degrees , the revs in turn would end up being higher than what they were at the moment, as for me putting 5k jets in ive only gone from 100 to 108 on primary and 147 to 153 secondarys and the motor runs shit hot, its a big improvenment, i might just be enjoying a new motor, but i reco'ed the carb and put the bigger jets in after i had the car running and driving and noticed a drastic improvement. if your a bit undecieded you should definately try the 5k jets and tell me differently, as raven said, the cam was bigger and i noticed it with cam ad jet changed. I havent tried to ditch the fuel cut-off solenoid like felix has told me but i'll do that now, could be an issue as it seems to hunt or surge for idle, and revs fine, dies, then picks revs up again to where it was before, ive dropped idle now but my missues wont be able to drive it so i'll up it but just looking for answers or tell tale signs

[coln72]

before getting rid of the fuel cut - try hooking the wires off it to the battery to see if it works.

 

By the way, just how small is this smallish cam, because my 5k would idle at 1000-1200rpm with my cam and factory twin carbs. It might just be where it idles?????

[Jimpoole]

ok so thanks for the response jimpoole but the jets are fine in the car it does NOT ping at all through the rev range, and yes it does still idle, just high, theres no point in me trying to even retard the timing to 8 because it'll just die,or run at like 2000rpm to hold 8degrees , the revs in turn would end up being higher than what they were at the moment, as for me putting 5k jets in ive only gone from 100 to 108 on primary and 147 to 153 secondarys and the motor runs shit hot, its a big improvenment, i might just be enjoying a new motor, but i reco'ed the carb and put the bigger jets in after i had the car running and driving and noticed a drastic improvement. if your a bit undecieded you should definately try the 5k jets and tell me differently, as raven said, the cam was bigger and i noticed it with cam ad jet changed. I havent tried to ditch the fuel cut-off solenoid like felix has told me but i'll do that now, could be an issue as it seems to hunt or surge for idle, and revs fine, dies, then picks revs up again to where it was before, ive dropped idle now but my missues wont be able to drive it so i'll up it but just looking for answers or tell tale signs

Why don't you try putting in the original idle jet only and see if that fixes the problem? That way, you will still have the power of the bigger jet and a good idle. Just an idea. You still need stoichiometric mixture of 14.7:1 if you are going to run a combustion engine, even if you have a lumpy cam or not (or so i believe).

[springersrolla]

i never changed power valve or idle jet, just primary and secondary jets so its not an idle jet problem, plus 5k idle jet is about twice the length of the 3k one, the car runs fine with those jets, the cam I'm puzzled about, the bloke i bought it off had no idea, i got the reciepts and it says cam regrind, and he said it's a little cam, hard to tell if it was a 20-60 just by idle note just cause of idle, especially when its high, so i have no idea. i'd say coln72 that u might be right just with a higher idle, i had the intentions of getting the exhaust shop to put an o2 sensor but they had no threadolets so when there in ill get one and run a stoich mixture gauge to make sure the motors running well through the range, but for now ill take it to a shop with a gas analysier and find out whats goin on, thanks for your input guys

[Felix]

You still need stoichiometric mixture of 14.7:1

 

That is on the cruise, not at idle. At idle the mixture will be richer than at cruise revs.

 

springersrolla has only made a small step up in the main jets. They shouldn't make a difference to the idle, as at idle the carb shouldn't be drawing on the primary main jet unless there is a problem.

 

Can you see fuel coming from the Auxillary Venturi (or boost venturi in the attached image) at idle? If so there is a problem with the idle circuit of your carb. If fuel is coming from the Auxillary Venturi at idle the carb is running on the primary circuit.

 

Edited July 12, 2009 by Felix

[Boost+k]

i highly dout that the jets would cause this problem... to me it sounds like there is no power to the cut off solinoid, so then youve tuned/adjusted it to make up for that and it will create problems like this, like said above unplug the solinoid and see if the car dies or idle goes higher or lower

[Jimpoole]

Well it would appear that I'm wrong and I stand corrected. My apologies.

Whatever you do, have fun with it.

[Felix]

Jimpoole, you're all good mate. :dance:

 

Have a look HERE for a good article on Air/Fuel Ratios. It is written more focused on EFI systems but really a carb isn't much different, just less precise.

[Jimpoole]

Jimpoole, you're all good mate. :dance:

 

Have a look HERE for a good article on Air/Fuel Ratios. It is written more focused on EFI systems but really a carb isn't much different, just less precise.

That's a fair good article.

So richening up will give you more power?

[Felix]

So richening up will give you more power?

 

On the main circuit, yes it will give more responsiveness, but possibly at the expense of fuel economy.

 

Really the only way is to find out by trial and error.

 

I've found that fitting a narrow band O2 sensor with a digital A/F ratio meter is an awesome tuning tool for carbs. Obviously it isn't as precise as a wide band setup, but it is infinitely better than shooting in the dark. Makes setting up a carb a couple of hour affair if you have a selection of jets available. The setup in my ke15 owes me just over $100 with a second hand O2 sensor, the kit and getting an 18x1.5mm nut (ground to match the curve of the exhaust) welded into the exhaust. If you are going to do this, use a heated 4 wire O2 sensor.

 

I'll see if I can dig up a few pics of my O2 meter setup off my other PC.

Edited July 13, 2009 by Felix