Lack of top end RPMbs in both 454bs under load

"I was referred to this site a

"I was referred to this site a year and a half ago when I purchased our 91 Carver 538 Montego, with twin '90 454 Crusaders. The problem I am going to describe is mentioned through out the discussion board, but is normally associated with one engine and not both.

The engine information is as follows:
C454RH SER# 86600
C454LH SER# 86550

The maximum RPM for both engines is about 3600. The compression, at the time of survey, was 119-124 for all cylinders in both motors. Temperature readings were 160 in the slip, and 170 under load.

Since purchasing the boat I have had the props repitched from 20/20 to 18/20. All fuel filters have been changed, to include the internal carb filter. The spark plugs have been replaced. The timing has been checked. The RPM's have been checked at the engine, in order to rule out bad tachometers.

The carbs are Quadra jets. The four barrels do open and remain open. The throttle linkage is opened all the way at WOT.

The problem is consistent whether fuel is pumped from both or either fuel tank. The RPM's do not jump around. Acceleration is smooth and even to 3600 where it ends. The engines run well with no other notable problems.

Any suggestions on where and what to look for next would be appreciated?"

either timing or high speed je

either timing or high speed jets are not right

"did prop change make any diff

"did prop change make any difference? bottom clean? would look at timing at full throttle (advance) and spring plates in carb. one engine can hold the other back, but both having problems at the same time unlikely. any other symptoms?"

"The prop change gained, maybe

"The prop change gained, maybe, 200 RPM. We were expecting 400+. I checked with Carver and they recommended 20/20 props.

The bottom is clean.

The distributor had been changed to an electronic conversion kit by a previous owner."

"I'm still thinking advanc

"I'm still thinking advance. were distributors replaced, or pertronics type? if points replaced, You still have mechanical advance. don't have specs in front of me, but W.O.T. timing should tell something. or as J.I.T. suggests, carb secondarys not coming on line."

was this always the case? &#40

was this always the case? (since You've owned boat)

"Yes, I have had the problem s

"Yes, I have had the problem since purchase. I am looking for information on the carburetors, and how to check and adjust the secondary jets. The previous owner stated that he had the carbs rebuilt/reconditioned. I am now wondering if they were not done correctly. I continue to solicit thoughts, ideas, and recommendations."

"CHECK ADVANCE WITH TIMING LIT

"CHECK ADVANCE WITH TIMING LITE. rev engine timing should advance. You can do this out of gear. can look up specs if You need. secondary jets not likely to plug. more likely spring plate binding, or overtite. thats the plate over the secondary bores, looks like choke, but spring loaded. need to check under load. the two rods that hang from it go into the jets. if it doesn't open, You won't go. You can hear the sec.s open in the engine room. get a helper and check it out. good luck, S."

sorry about capitals. was not

sorry about capitals. was not for emphasis. didn't realise capslock was on. (have to look to type)

"CHECK ADVANCE WITH TIMING LIG

"CHECK ADVANCE WITH TIMING LIGHT. I am using caps for emphesis. Total advance should be in the 30+ degree range, maybe as high as 36. If your initial timing is set correctly and you are not acheiving this much advance, you have found the problem. Is that compression within spec? Depending on the engines I would expect to see 150-175.

Also check the gear ratio, experience tells me in a 38' boat it should be 2.68:1. I would not be alarmed if they are 2.5 since Carvers are so flat but I would confirm that with Carver if they are.

Are the props cupped? The degree of cup can mean several hundred RPMs.

Good luck,
Rick"

"Rick,
How do you change the

"Rick,
How do you change the advance? I know that the timing at idle is at spec. The numbers were not in the 30's. As RPM increases timming was closer to TDC.

The gear ratio is 2.6?:1 and props are cupped"

"The gears appear to be correc

"The gears appear to be correct but you are not acheiving full timing advance. I would suspect the problem lies in the distributors. I'm not that familiar with this distributor so someone can correct me if I'm wrong, but the full advance can not be changed, it is programmed into the distributor. If it had mechanical advance you could change the springs. It sounds like either the wrong distributor components were used, something is installed incorrectly or something has malfunctioned. The timing should reach full advance at 2500-3000 RPMs. It will not advance any more after that, but should not decrease either. Also prop cups are graded 1-5, 5 being the heaviest. Each grade of cup relates to 100-150 RPMs, depending on the package.


Get the service manual and determine the full advance for this motor. If you feel compitant to try this, and have some qualified friends, you can manually advance the distributors to the correct full advance while underway. If the performance improves to what it should be, you know you have found the solution.

This is where the disclaimer comes in: PLEASE USE CAUTION. HAVE A QUALIFIED OPERATOR RUN THE BOAT. HAVE SOMEONE ELSE ONBOARD TO RELAY COMMUNICATIONS BETWEEN THE BRIDGE AND THE BILGE. KEEP CLEAR OF ALL MOVING PARTS. ENGINES MAY STALL AND WILL NOT RETURN TO PROPER IDLE WITHOUT RETARDING THE DISTRIBUTORS TO CORRECT BASE TIMING.

Good luck
Rick"