You will find some background info here: http://forums.iboats.com/showthread.php?t=201288
After attaching fittings to the intake manifold, I was able to get the vacuum readings. After engine is warmed up, I am getting 14"HG at 600rpm. While some references indicate, that this is the very bottom of the good range, given Tony's response, it seems low. It does hold steady, with only slight variation +- 0.5"hg. Reading were taken with a new $20 Accutron gauge. My old (20+ years) noname gauge, only read 10".
I have read numerous links on the web dealing with vacuum readings. Most indicate that it is an indication of bad rings! But also lists many other items. Below, is what I have done so far, and near the bottom my forward plan for continued diag this weekend. For now, I have scrapped hauling the boat the three hours to camp, but might put it in a local lake on Sunday.
Done so far:
- I used carb cleaner to look for vacuum leaks around intake and carb, did not find any. But, took some new pait off carb base
BTW, web reading indicated the prefered method for finding leaks was with propane. Could a plumbing portable torch cylinder be used for this? Is it better than carb cleaner? I also hear a slight whissle when my head is turned a certain way. I can't seem to issolate. It does not seem to be coming from carb (ear near airhorn).
- Rechecked base timing and is @ 10 degrees BTDC, per spec.
- RPMs above are from an Accutron gauge, not boat tach.
- The flex carb adjustment tool did not fit the idle mixture screws. I will pick-up a pair of narrow needle nose pliers to get at them. I do believe this is part of the low vac readings issue. If I provide some choke, the rpms do increase. This would lead me to believe it is too lean, or vacuum leak.
Plan:
- Get the mixture screws adjusted. If I can't make it bog from a too rich adjustment, probably indicates leak. I believe this is key, given the choke test increases rpms.
- Pull intake manifold and redo installation/torque sequence.
- Re-adjust hyd lifters. I carefully did the non-running procedure per merc manual. I do have rocker clips, so could do the running method.
- Pull plugs and examine, but doubt that will say much at this point. While I have rechecked oil to make sure water was not getting in, maybe the plugs might indicate that.
- Do a compression check. For this weekend it will be with my old cheapo gauge. I would have to buy parts, etc to do a leak down. If I have to go there, it will be after this weekend.
If the idle mixture screw adjustment gets the readings in 16-18" range, and it is not giving the choke/lean indication. OK to lake test on Sunday? or am I getting too paranoid?
I appreciate any thoughts or recommendations.
After attaching fittings to the intake manifold, I was able to get the vacuum readings. After engine is warmed up, I am getting 14"HG at 600rpm. While some references indicate, that this is the very bottom of the good range, given Tony's response, it seems low. It does hold steady, with only slight variation +- 0.5"hg. Reading were taken with a new $20 Accutron gauge. My old (20+ years) noname gauge, only read 10".
I have read numerous links on the web dealing with vacuum readings. Most indicate that it is an indication of bad rings! But also lists many other items. Below, is what I have done so far, and near the bottom my forward plan for continued diag this weekend. For now, I have scrapped hauling the boat the three hours to camp, but might put it in a local lake on Sunday.
Done so far:
- I used carb cleaner to look for vacuum leaks around intake and carb, did not find any. But, took some new pait off carb base
BTW, web reading indicated the prefered method for finding leaks was with propane. Could a plumbing portable torch cylinder be used for this? Is it better than carb cleaner? I also hear a slight whissle when my head is turned a certain way. I can't seem to issolate. It does not seem to be coming from carb (ear near airhorn).- Rechecked base timing and is @ 10 degrees BTDC, per spec.
- RPMs above are from an Accutron gauge, not boat tach.
- The flex carb adjustment tool did not fit the idle mixture screws. I will pick-up a pair of narrow needle nose pliers to get at them. I do believe this is part of the low vac readings issue. If I provide some choke, the rpms do increase. This would lead me to believe it is too lean, or vacuum leak.
Plan:
- Get the mixture screws adjusted. If I can't make it bog from a too rich adjustment, probably indicates leak. I believe this is key, given the choke test increases rpms.
- Pull intake manifold and redo installation/torque sequence.
- Re-adjust hyd lifters. I carefully did the non-running procedure per merc manual. I do have rocker clips, so could do the running method.
- Pull plugs and examine, but doubt that will say much at this point. While I have rechecked oil to make sure water was not getting in, maybe the plugs might indicate that.
- Do a compression check. For this weekend it will be with my old cheapo gauge. I would have to buy parts, etc to do a leak down. If I have to go there, it will be after this weekend.
If the idle mixture screw adjustment gets the readings in 16-18" range, and it is not giving the choke/lean indication. OK to lake test on Sunday? or am I getting too paranoid?
I appreciate any thoughts or recommendations.
