High speed miss...

[John D.Fullerton]

Hi Guys, need some help...I have a 87 comp TS6m with a 351 PCM.

- It starts, purrs while idling and up to 35mph and 3100rpm. When I call for more power at this speed beyond 35mph there seems to be a 1 or 2 cylinder break down.
- I have replaced all plugs, water separator and inline fuel filter. A new electronic fuel ignition kit was installed 5 running hrs. ago. I have also cleared the screen in the fuel tank and line to carberator.
-When calling for power the secondaries open up with ample fuel flow.
- I believe I have virtually eliminated as a fuel related problem.
- I have also adjusted the timing and no change.
- plug wires are fairly new, could there be a wire breakdown?

Has anyone had or heard of a similar problem and resolved it?

Any suggestions would be appreciated...

John D.

[riveredge]

I have seen the fuel line itself collapsing under similar circumstances - try running the boat off a separate fuel supply (little portable outboard tank or something) and see if you get the same symptom. It's one thing to try, anyway.

[Salty87]

holley carb?> you might check the power valve. cheap and easy

[FoiltechLaunch21V]

Fuel line and/or the power valve Could be the culprit. Both are fairly cheap and somewhat easy to fix/replace. IMO


Good Luck!

[OUI]

Check to make sure the advance machanism in the distributor is working properly.

[DKJBama92Mariah]

Does it do the same when you rev it in neutral? If so its probably ignition related. If not, suspect fuel flow/carb problems.

Sounds like you've done everything but rebuild the carb. When was the last time it was rebuilt?

[John D.Fullerton]

Hi Guys--- sorry for the late response, since your responses last week and your suggestions, have done the following,in addition to the above-- replaced the fuel line,rebuilt the carb, it was clean ,but a new kit anyway,did a pressure test on the fuel pump, it cheked out ok. Changed the plug wires . Still no cigar! After replacing the carb,I took it out for the first run- I hit 41mph Hallaluya !! and more throttle to go ! The 2nd run, with a skier, back to 35mph and missing Am rather perplexed to say the least ! Am beginning to wonder now if there maybe intake manifold leak ? AS I said before -- from start-up to 35mph this 351 prurrs tike a kitten ! - but as soon as I run a barefooter or slalom its a no go ! Any how will keep looking, thanks for your suggestions,and any further thought would be appreciated ! Perplexed in Northern Ontario! John D.

[DKJBama92Mariah]

Hi Guys, need some help...I have a 87 comp TS6m with a 351 PCM.

- It starts, purrs while idling and up to 35mph and 3100rpm. When I call for more power at this speed beyond 35mph there seems to be a 1 or 2 cylinder break down.
- I have replaced all plugs, water separator and inline fuel filter. A new electronic fuel ignition kit was installed 5 running hrs. ago. I have also cleared the screen in the fuel tank and line to carberator.
-When calling for power the secondaries open up with ample fuel flow.
- I believe I have virtually eliminated as a fuel related problem.


I'm assuming from your silence on the issue that the engine doe not do this in neutral. If it is a timing problem on a regular distributor, it would present with and without a load. Fuel flow problems typically show up only at speed.

We still need to eliminate fuel flow as a problem. You need to check you're fuel pressure while this is happening. Meaning rig up a fuel pressure gauge between the fuel pump and carb and have someone watch it while you drive and give er hell. Fuel pressure should not drop below 4 psi.

Possible fuel flow restrictions you haven't mentioned:
1) Collapsing fuel line as Foiltech and riveredge already mentioned - if it hasn't been replace in the past 10 yrs or so, it needs to be done anyway;

2) Clogged anti-siphon valve at fuel tank - this prevents fuel from filling up the bilge if you have a cut fuel line, it can get clogged with gunk and restrict flow (your boat may or may not have one of these);

3) Clogged fuel tank vent line - check this by running with gas cap off;

4) Clogged screen on fuel pickup in the tank - pull fuel pickup from tank and clean screen.

Not to make a scapegoat out of E10 ethanol fuel, but we have seen an awful lot of fuel flow issues this season. I have the feeling that a lot of the problems are related to the transition E10 and the crud it loosens up in the tank. I've even had fuel flow issues myself.

Quick question: when it is doing the bogging thing, does the temp gauge rise at all?

[John D.Fullerton]

Dkjbama 92 Mariah

Again, thanks for your reply, and my apologies for my once again – late reply. In the interim have been doing much trouble shooting and finally a resolve.

Believe me, with what we went through to resolve the high speed miss – I can tell you what is not wrong with this boat!

The problem was not fuel related. I had thought that the previous owner has installed a new electronic conversion kit. He did, but replaced an earlier installed kit. This was done by a local marina in Lower Michigan just before I bought the boat. The electronic conversion was not installed properly. The installer obviously didn’t know what he was doing. To this point we had eliminated everything except the electronic module or kit. I purchased a new kit with instructions that were very specific. The ignition has a ballast resistor. The ignitor system must be connected to the Ballast resistor. This was not done, resulting in too high voltage thus burning out the electronic conversion kit and distributor. We replaced the distributor but didn’t think as suspect. Once we determined this, we thoroughly checked all the wiring, hooked up a new kit according to the instructions. Voila!!! Success! The engine runs awesome. We just need to tweak the timing and we are home free. Am now getting 41 mph and no miss!!

Many thanks again for your help. Hope this helps someone in a similar dilemma.

Regards
John D