Triple Mikuni thread

[Mike]

This manual would be a great addition to the downloads area. Let me know where you guys have the file buried.

[steve91tt]

What is your wideband telling you? I had a fairly bad transition stumble when I first installed my Mikuni's. I solved my issue by adding more fuel to both the idle and main circuit. I also had to purge the air out of the accelerator pump system as Todd mentioned. With a few minor jet tweaks I now have zero hesitation at any RPM or throttle position. It's been my experience that these cars tend to idle and accelerate/transition best at 11-12ish AFR with Mikuni's. Keep at it, once you get them tuned you will love them.

[madkaw]

steve,

I don't see how to richen up the idle without installing a bigger primary jets.

I'd like to know what jets you are running?

Did you work the accelerator pumps while on the car or off?

At this point I am thinking of pulling off the carbs and holding the butterflies open to see the pumps working.

[steve91tt]

I have the following setup on my L30...

44mm carbs

34mm venturis

150 fuel jets

210 air

57.5 pilots (1.5 turns out)

1.8 needle/seat

45 pump jets

I ran the same setup on a bone stock L24 with a set of 145 fuel jets.

You can work the air out of the accelerator system by opening and closing the throttle while the fuel system is pressurized. You can do this when the engine is on or off. I did it by driving around stabbing the throttle periodically. It's a little tricky to see if the accelerator pumps are working but you might try taking off the air horns and using a mirror to look down the bore.

If you are lean at idle at 3 turns out then you might need bigger pilots but Todd is the guy to ask. Does your idle change the same for all 6 cylinders as you close your adjustment screws? On my L24 I found that some cylinders reacted differently than others. Eventually I found that I could get the smoothest running engine by adjusting each cylinder individually so that screwing the pilot adjuster in 1 turn had the same effect on the engine. In other words, I'd turn the adjustment screw in 1 turn and record the idle change for each cylinder one at a time. I would then adjust the individual adjustment screws so that one turn in resulted in the same effect on the engine. This resulted in some cylinders being set at 1.25 turns out while some were set at 1.75 out. I don't think this is your issue but you can use this technique to determine if all of the idle circuits are working the same. If you have a vacuum leak or some other sort of issue with one carb you may be able to spot the problem child this way.

Just my $0.02.

[madkaw]

This manual would be a great addition to the downloads area. Let me know where you guys have the file buried.

Here you go Mike!

http://forums.hybridz.org/index.php?app=core&module=attach&section=attach&attach_id=2126

[madkaw]

I have the following setup on my L30...

44mm carbs

34mm venturis

150 fuel jets

210 air

57.5 pilots (1.5 turns out)

1.8 needle/seat

45 pump jets

I ran the same setup on a bone stock L24 with a set of 145 fuel jets.

You can work the air out of the accelerator system by opening and closing the throttle while the fuel system is pressurized. You can do this when the engine is on or off. I did it by driving around stabbing the throttle periodically. It's a little tricky to see if the accelerator pumps are working but you might try taking off the air horns and using a mirror to look down the bore.

If you are lean at idle at 3 turns out then you might need bigger pilots but Todd is the guy to ask. Does your idle change the same for all 6 cylinders as you close your adjustment screws? On my L24 I found that some cylinders reacted differently than others. Eventually I found that I could get the smoothest running engine by adjusting each cylinder individually so that screwing the pilot adjuster in 1 turn had the same effect on the engine. In other words, I'd turn the adjustment screw in 1 turn and record the idle change for each cylinder one at a time. I would then adjust the individual adjustment screws so that one turn in resulted in the same effect on the engine. This resulted in some cylinders being set at 1.25 turns out while some were set at 1.75 out. I don't think this is your issue but you can use this technique to determine if all of the idle circuits are working the same. If you have a vacuum leak or some other sort of issue with one carb you may be able to spot the problem child this way.

Just my $0.02.

Well I have established for sure that not all of my accelerator pump nozzles are shooting fuel. I decided to remove everything to replace my intake gasket-since I reused my old one. The old gasket didn't show leaks under idle, but I needed to eliminate any possibilities or guessing.

Since I removed the carbs from the intake i could have a clear view of what's going on. #1 cylinder had NO fuel coming out of the nozzle, while #2(same carb) shot out 3 feet in the air-and almost in my eye:stupid:

The second carb was a little better, but small amounts of tip-in of the throttle showed that the nozzle wasn't 100%. You should see a bit of projectile fuel with the smallest of throttle movement. Any lack of fuel would show up as a dead spot in transition while driving.

I pulled out the nozzles to check cleaniness and make sure all ports were clear. Todd also told me to make sure the packing washer is there under the nozzle when you remove it. Another note about nozzles are that they are keyed and will only fit in the carb body one way. They are keyed to make sure the squirter hole faces down the port. When you drop the nozzle back in the carb body-it should fit flush with the top. The picture is the nozzle IMPROPERLY installed-notice how it sticks out!

I did drop the cover off the bottom of the carb that covers the diaphram of the accelerator pump, and it looked great. So for some reason I am not getting fuel into the nozzle cavity so it will squirt out.

Steve, I tried pumping the "air" out by filling the body with fuel and operating the throttle-MANY TIMES! I could only get fuel to come out one of the nozzles, I must have a blockage somewhere or the check ball is stuck, not sure how to clear that up, but I haven't done any compressed air yet.

After talking to Todd, I readjusted the floats. See the picture for proper adjustment. Todd said he likes to see 13mm between the lid(with gasket installed) and the top of the float. Measure at a point parallel with the brass tube in the background-roughly in the middle. The manual calls for 12mm-12.5mm.

[steve91tt]

Sounds like you found your problem. I'm looking forward to hearing what's stopping flow to some of the accelerator circuits. Keep us posted.

[madkaw]

Well I took accelerator pumps and nozzles out and blew some compressed air thru the passages and looked things over. Really couldn't see anything that would cause any problems, but there was something somewhere, because the nozzles are all shooting equally:beer:

Then I pulled out the pilot screws and bad news(see pic). This is why you don't use any force whatsoever when bottoming out the screws. Someone really cranked on these and actually left a step in the mild brass screws. Todd has 6 new ones coming! I have some larger pilot air jets coming also incase.

Soooo-while I am waiting around for parts I decided to put some heat barrier on my intake. Not sure about some of the other heat shields out there, but the one I made doesn't go all the way under the intake, just the carbs. I got some Thermo-tech adhesive backed stuff and wrapped the bottom side of the intake.

[steve91tt]

Good news, easy fix! I like your heat barrier idea. Let us know how it works out. I'm always looking for anything that will keep the carbs cooler here in Texas.

[Zedyone_kenobi]

I am not sure keeping heat from your intake is a good idea. The extra heat into the manifold is needed to keep the fuel a vapor. There are many paper written about this. In a nutshell, keeping the intake warm helps keep the fuel in a vapor state. Too cool, it can puddle and not stay vaporized. Keeping the carbs cool is good, but a properly warm intake is good idea in many cases.

for the most part, I think wrapping the intake will only prolong how long it takes to get to operating temperature. Just a thought.

[LeonV]

I am not sure keeping heat from your intake is a good idea. The extra heat into the manifold is needed to keep the fuel a vapor. There are many paper written about this. In a nutshell, keeping the intake warm helps keep the fuel in a vapor state. Too cool, it can puddle and not stay vaporized. Keeping the carbs cool is good, but a properly warm intake is good idea in many cases.

for the most part, I think wrapping the intake will only prolong how long it takes to get to operating temperature. Just a thought.

I agree, at least for a carb'd car. Keeping the intake warm is a necessity, unless you want to run really rich. This is why air-cooled engines require overly rich mixtures, as they have a huge "Tau layer" in their intake, "Tau layer" referring to the liquified fuel film in the intake. Rich mixtures must be used to cover up any lean holes during operation. It may work okay for racing applications, but you may be better off going without.

Nice job though, should be a good experiment nonetheless! You'll never know until you try. Those triples will be roaring soon enough!

[madkaw]

Good point guys. Honestly, I didn't think my wrap job would do anymore then keep the extreme heat from the header away from the bottom of the intake and keep the fuel charge a bit cooler. The wrap is only on the bottom half of each runner, and I believe there will still be plenty of heat in the intake.

I also thought I have searched and found guys that have run a heat shield all the way up against the head, so this would be different?

I would also consider the length of my intake runners-2"- maybe. Now how long are the VW runners. Just think how far the Mikuni pumps spray fuel-direct injection!! Not sure if any pooling is going to happen on this intake.

I was actually worried more about heat transfer from the intake to the carbs.

Besides-you know how long it took to make those weird patterns to wrap around that intake-they're staying-