Mercruiser 57 LX Thunderbolt idel and timing problems

"I have a 1997 5.7LX with the

"I have a 1997 5.7LX with the Thunderbolt ignition and Rochester 4 barrel carb, which ran great some days and would not even start on others. On one of the days it would not start I found that I had power going into the ICM but none passing through (plus it somehow had water coming out of the ICM) so I replaced it. This is where the fun started. The original part was 806957-4 which even the factory had no record of such a part number so they insisted that the part was a 806957t4 which has been superseded (of course) to part number 807264A01 which is a conversion kit, so that is what I ordered. The old part said right on it that it was for the 5.7LX; however upon opening the new part the instructions (which were in the plastic which stated no returns if opened) stated that it was for all 5.7 within a certain serial number range (which my motor was in), but for engines with 2 barrel carbs. I called several dealers and the factory and they all insisted that this was the correct part, and that it was used for both 2 and 4 barrel motors as this is what both the 5.7 L (2 barrels) and 5.7LX (4 barrels) were superceded to. At this time I also replace the plugs, distributor cap, rotor, gasket, ignition sensor, and fuel filter / water separator right away. Now two problems:

#1) the motor is having a very hard time starting as it sounds like the timing is set too high, but it runs great once stated. If I back the timing off it starts easier but falls on its face. I have grounded out the purple and white wire to set the timing and adjust the carbs idle speed; however:

#2) the idle speed will not drop even when bypassing the module. It is up around 2000 RPM, and I cannot get it to do down. It will not respond to the idle screw. I have even removed the linkage to make sure that this was not the problem. The choke appears to be working properly and not hanging up.

Sooooo help! What next? Could this all be caused by the module which they insist is correct or am I doing something incorrectly? Of course there are no returns on electronic parts, even those costing $400.00, and which could be causing the problem. Is there some other way that I should be bypassing this new part? Please help, the season is so short up here and I do not want to miss another weekend."

"Make sure the water is out of

"Make sure the water is out of the old one and it is dry,seal it and try it. If it works and everything returns to normal then the ECM they sold you is not correct. Then you need to find the correct ECM. How did water get in the old one?"

"Aside from what Not Me said,

"Aside from what Not Me said, See if your secondarys are closing on the carb.
if not completely close it will also cause hard starting and RPM Idle....... Water?"

"It was late and I was thinkin

"It was late and I was thinking one thing and typing another, the carb is a afb carter / weber 4 barrel."

"Remove the control cable from

"Remove the control cable from the throttle linkage then recheck the idle. Make sure the idle screw is making correct contact and that all carb linkages are free and undamaged. Some carbs have fast idle linkages that sometimes need adjustment or get slightly bent or stuck. Have carb cleaner handy to free these up. Look at the throttle plates. The carb will only idle high if they are open. Note how your small gold linkages attach to the carb and what they operate. You want the carb plates at rest with no binding. When the throttle lever is vertical, try to put the throttle control cable linkage back on. Do you have to stretch the throttle plates open to attach it? If so, there is an adjustment to add more slack on the cable bracket. There should be no spring pressure applied to slide the T cable linkage on. Just idea starters... hope one helps."

"The fuel pump is working fine

"The fuel pump is working fine and the carb appeared to be fine looking in from the top. As a last resort I took it off only to find that some knot head had trashed it. The plates were bent (one would close the other was open 1/8"), and that there was a bent shaft with a shear off screw head. The plates also had vice grip teeth marks on them, as if someone tried to straighten them out. I just ordered a rebuilt carb from Fly Fishing Carburetor in Largo FL ($228 plus $88 core...what a deal!) and should have it on Sat morn. The timing is working, but it is still hard to start which, I assume is do to the carb issues. I hope this is the end of the gremlin chase."

I'll bet the spark advance

I'll bet the spark advance is stuck at too far advanced. THat would account for several of the symptoms. Put a timing light on it and rev the motor. The advance should move about an inch on the pulley.

Jeff