Crossflow guys NEED HELP

[FlowMaxx]

I am trying to help my friend get his 2.6 GT to run right and am running out of ideas. Over the winter the motor was dissasembled and taken to Ruck where it was bored, had 3 sleeves and was properly set up by Ruck to run wiseco pistons. The intake and exhaust ports are opened up slightly, but are at the proper heights. He is running 638/39 heads cut 25 thou. Good tuner, can removed and exhaust relieved. mid section dried up with 1/4" holes drilled for water pump cooling. 93 octane with a 50/50 mix with race gas and properly broken in with cheap 2 stroke oil, but now running XD100. Running a Holley fuel pump, which worked fine all last summer on a 140. The boat is a very light and rock solid Hydrostream Vector.

The problem: the motor pulls really hard up to 6200 where it hits a wall and seems to be misfiring or 4 stroking. During testing and diagnosing, the entire electronics have been switched out including 2 different sets of known working and unlimited cdi boxes. Still the same. Then we worked on jetting. Running 3 stage 1 3/8 carbs with 70C main jets. The full throttle plug chop shows lean, however, when you bump the primer at full speed, it boggs and does not pick up at all. then we bumped up two sizes and had the same result. Plug chop still shows lean. Is is behaving like it is 4 stroking, which it should with these big jets. Even tried a set of good 1 5/16 carbs---NO change. The only thing I am unsure about is that he rewired the key switch to a on dash switch with a button to start it. Everything works fine including the kill switch.


Please offer suggestions as I am unsure of where to go from here.

[flabum1017]

Almost sounds like a rev limiter but those did not have limiters in them. If your'e running lean, then it's fuel delivery......you got a gauge on that pump?

[FlowMaxx]

No guage. Can one be had at a local auto parts store? The carb numbers are:

On the metal tab screwed to the float bowl:

398404
MX
10 I L

Stamped on the carb body:

332166

Any suggestions on what the problem could be are appreciated. After messing with this thing for weeks, the frustration level is high and our brains are a little mushy on this topic. I am sure you guys have been there at one time or another. We are going to let is sit for a week while I gather suggestions from you guys so we can leave no stone unturned next time we are on the lake. Thanks in advance.

[BarryStrawn]

How do you know the ignition is not limited? Try a much smaller prop to confirm the rev limiter.

The part number on the carb tag is for a 1987 150. Was 1 3/8" cast into the inlet face?

[Baja16]

How old are the CDI boxes you tried, i have seen some OMC engines that were originally non-limited but the replacment boxes were.

[Laker]

Tell your buddy to throw everything in the garbage and take up hang gliding:reddevil:

[Forkin' Crazy]

Sounds rich to me. If it is really rich, it will wash the plugs and will not color them.

If you have the go pedal to the floor, then ease up a bit, and it picks up RPMs; that could be an indicator of a fat mixture.

I am running 63 mains if I remember right and turn a GT Xflow 6800 to 7000. Some of the GT carbs take larger jets though.

When you say entire elec system, do you mean coils too? Do a spark test with the tester set at 7/16".

I don't trust any high perf electric fuel pump with out a regulator and a gauge. I have had the red pumps put out too much pressure.

[FlowMaxx]

How do you know the ignition is not limited? Try a much smaller prop to confirm the rev limiter.

The part number on the carb tag is for a 1987 150. Was 1 3/8" cast into the inlet face?

When we switched the electonics and the boxes were off my motor that spun 6900 RPM with no issues. The carbs do have 1 3/8 cast on the front of each.

[Riverratt]

The XP/GT had a 6200 limited pack on one side.

[FlowMaxx]

http://i306.photobucket.com/albums/nn280/FlowMaxx/101_4008.jpg

This was a plug that was previously used in a different motor. Before the plug chop as shown, the tip was black like the outer ring.

[FlowMaxx]

http://i306.photobucket.com/albums/nn280/FlowMaxx/101_3995.jpg

This was a brand new plug. Idled for a few min. Warmed up, then did full throttle plug chop.

[flabum1017]

Is there a dash numer right after the part number on the power packs?

[FlowMaxx]

These are the original ones we ran. They were replaced with a known and tested set of unlimited packs. Identical results

http://i306.photobucket.com/albums/nn280/FlowMaxx/101_4040.jpg

[FlowMaxx]

http://i306.photobucket.com/albums/nn280/FlowMaxx/101_4039.jpg

[FWP3LCF]

Have you tryed the timing???

[FlowMaxx]

Timing was at 28 and backed it down to 24. No noticable difference

[Streamin101]

Do you have the right coil pluged into the right sparkplug, it sounds like a no brainer but i have experienced this before.

[Forkin' Crazy]

This was a plug that was previously used in a different motor. Before the plug chop as shown, the tip was black like the outer ring.


So was it as dry as in the pic when it came out of the motor????

[FlowMaxx]

So was it as dry as in the pic when it came out of the motor????


yes. All 6 looked very similar. Pulled the teather @ WOT. Plug chops looked the same with 70c's in all 6 AND with 72c's in 1256 and 74c's in 3 and 4.

[FlowMaxx]

Do you have the right coil pluged into the right sparkplug, it sounds like a no brainer but i have experienced this before.

yes they are correct

[neveredge]

To the best of my knowledge the only true unlimited crossflow packs are the C.D.3/6 582138. You need 2 of these to make it work.

You are running limited packs.

[Forkin' Crazy]

I don't care what packs you have, if the plugs are that dry, it is lean.

Sounds like a fuel delivery problem. Put a pressure gauge after the pump. What kind of filter(s) are you using?

[flabum1017]

I don't care what packs you have, if the plugs are that dry, it is lean.

Sounds like a fuel delivery problem. Put a pressure gauge after the pump. What kind of filter(s) are you using?


Yep..... put a gauge on it and see if you still have gas at WOT :rolleyes:

[FlowMaxx]

To the best of my knowledge the only true unlimited crossflow packs are the C.D.3/6 582138. You need 2 of these to make it work.

You are running limited packs.


I have a a 582138 that is limited.

[racer]

If you have a 582138 that is limited it has something wrong they were unlimited boxes. Check fuel pressure.

[FlowMaxx]

If you have a 582138 that is limited it has something wrong they were unlimited boxes. Check fuel pressure.

I have wondered about that because I have another that is unlimited. I will discard the bad one then.

What is the acceptable minimum and maximum pressure ranges? We will try to get our hands on a guage this week. Any suggestions on the guage and where to get one?

Thanks guys.

[flabum1017]

7 - 9 psi @WOT

[Laker]

Contact Randy here.... http://www.performanceunlimited.com/
He had the liquid filled ones that never fail.
I have found Anything over 6psi can make the motor go rich

[FlowMaxx]

Will call Randy tomorrow for the guage. What would be the minumum pressure needed?

[Forkin' Crazy]

7 - 9 psi @WOT
That is too much. I run 3.5 to 4.0 psi with a Mallory pump and bypass regulator. Much more than that and you will blow the needles of the seats.

[FlowMaxx]

He got a guage from performance unlimited, thanks Chris. 5.5 psi with the motor off. Will test under various loads tomorrow.

[FlowMaxx]

OK, just found out that purple wire was disconnected on the ignition switch. My manual shows this wire going to the voltage regulator. I would assume this is a problem, although the motor starts, runs and shuts off just fine without it connected. Will connect it and see what happens.

[FlowMaxx]

Ok, Connected the purple wire today. This time I drove the boat. We put on a 21 pitch ski prop and it would hit the wall at 6000, but if I stayed in it, it would break through and spin up to 7k with a miss. Toward the end of testing, after trying the primer etc. I backed off the pedal just a touch, as Paul suggested, and the miss went away and it pulled clean up to 7k. will be down jetting 2 sizes tomorrow and we will see what happens. Oh, and we did a plug chop ak 5k with the primer button on for 5 sec. prior and the plugs still looked the same.....go figure.

Thanks for all your help guys.

[flabum1017]

Pulling back and gaining RPM.......classic lean.....how was the fuel pressure with the pedal to the metal?

[bw1969]

I'm running a 2.6 x-flow with the ports opened a bit, and I have 67 main jets in it. Not sure what model carbs but they are 1 3/8 inches. Timing is also set at 24 degrees. I can run it up to 72-7400 rpms without any problems, but your dry plugs are bothersome.

[Laker]

Does running XD100 make plug reading more difficult?

[FlowMaxx]

Pulling back and gaining RPM.......classic lean.....how was the fuel pressure with the pedal to the metal?

OK now I am confused. Paul says fat, you say lean. Who is right? I do not want to burn it down on speculation. It does not respond to larger jets or primer button at top rpm. Primer further bogs it down instantly. Plugs still look lean with a plug chop with the primer button on for 5 sec. Fuel pressure is about 4 psi at top RPM.

[terry taylor]

HI. plug chop #1 looks regular #2 looks leaner but could be the photo . You retarded the timing to 24 with no change, turn it back even more for safety until any issues are corrected to satisfaction thanks.

[BarryStrawn]

It think if it was that lean you would have stuck or holed a piston by now. As noted in your first post, it sounds like it is 4 stroking.

I'm not nearly smart enough to tune over the internet but I would jet it down one or two sizes and see what it does. If it improves, go smaller. And keep the small prop on it, less load is good until you get it running right. Then finish up your tuning with the big wheel.

[racer]

An overly rich cross flow will show lean on the plugs you need to look at the pistons, if you back off slightly and it gains rpm it is rich. You should only change jets one size at a time and generaly they like numbers 4 and 6 one size larger.

[FlowMaxx]

Thanks a ton everyone. Ran today with 67's on 1, 2, 5, 6 and 69's on 3 and 4. It ran great. Pulled over 7k with no problem. We are going to bump the middle ones down 1 size and call it a day. Plugs show a little rich, but we're ok with that for pleasure use for now.

again THANKS

:cheers: