Aq271c Engine wont rev past 2000rpm

[Sam Jenkins]

Hi I have a aq271c which required quite a bit of work when I bought the boat. But the engine won't rev over 2000 rpm when in gear. ( will rev freely out of gear)
Ive replaced distributorcap, rotor,leads plugs, fuel pump and carburetor from a holley 1406 to a elderbrock 1409. Ive also removed the rev limiter as this was stopping the engine from firing. All linkage is moving freely and opening up.
Has anyone experienced this and solved the issue.
This is the distributor
Many thanks Sam

 

[alldodge]

Have you checked compression?
What pitch prop is on the drive?

 

[Sam Jenkins]

Yeah I think I should check compressions again.
These are the numbers on the props but I'm not sure what they correlate to
Cheers

 

[alldodge]

Never have understood the numbering on VP props

My thought is maybe its over propped if the compression is ok (150 psi). If compression is low, then its just a tired motor

If the fuel is old (more then 1 year), this will reduce power if its E10

 

[Scott Danforth]

The motor will rev freely in neutral with only 3 of the 8 cylinders firing.

You most likely have a fuel issue

The stock dizzys are junk. Besides being costly for bits, the caps foul quickly. I replaced mine with a Mallory unit

The stock carb is supposed to be a 4150 holley at 715cfm. 72 front gets and staggered 80/90 rear jets. I ran mine after the cam change with 74/92

Do a compression test. You should be between 135 and 150 psi across all cylinders

You need to verify fuel pressure and make sure your dizzy cap and rotor are new

Check your fuel vent

Never have understood the numbering on VP props

My thought is maybe its over propped if the compression is ok (150 psi). If compression is low, then its just a tired motor

If the fuel is old (more then 1 year), this will reduce power if its E10

Depending on hull, props may be B3s-B6s. I ran B5s and B6s on my 3500# dry / 4300# wet boat

 

[Sam Jenkins]

Cheers for your replies,the whole fuel system has been renewed unless I have a faulty fuel pump or faulty carb. I also did fit a new cap rotor and coil( possible bad faulty new coil?)
Is it possible if the distributor isn't advancing the timing I would get these issues? Cheers

 

[Scott Danforth]

Its never the coil

Look at the mechanical advance weights. They either move or they dont

If it wasnt advancing, it would at least make it to about 3500 rpm

You still have the wrong carb compared to stock, however in proper tune, you have about 260hp with the 1409 vs the original 275

 

[alldodge]

Is it possible if the distributor isn't advancing the timing I would get these issues?

Use a timing light and see if it advances

 

[Sam Jenkins]

I just checked the mechanical advance weights would you say this looks normal apart from the rust cheers
One spring is stronger thet the other

 

[alldodge]

Unable to say, its moving just don't know if its enough of to much. Always check with a timing light. Many auto parts stores let you borrow one

 

[Scott Danforth]

I just checked the mechanical advance weights would you say this looks normal apart from the rust cheers
One spring is stronger thet the other

one spring is stronger than the other with the advance on the stock dizzy. there are two steps in the advance for the engine

 

[Sam Jenkins]

Compressions are good range between 150 and 160 psi hot and cold. Ive rigged up a pressure guage to measure the pressure comming out of the mechanical fuel pump could any one verify what this should be?
Once I've done this il check the timing.
The plugs look like the engine has been running rich

 

[alldodge]

Fuel pump pressure 4 to 8 psi, don't think that's the issue
Checking timing and advance

 

[Sam Jenkins]

Fuel pump pressure 4 to 8 psi, don't think that's the issue
Checking timing and advance

Yeah fuel pressure was 5.5 psi. I checked timing out of gear. The timing set to 6°btdc at idle and advancing to 23° btdc at 3000rpm.
Im starting to think it might be the Edelbrock carb ( which was new) which is supposed to be matched to the engine but un sure of what the jettings are supposed to be.
Even if the drive had a a lower ratio surely It wouldn't loose 2500rpm

 

[Scott Danforth]

your mechanical weights may not be not fully traveling. you should be at 28 degrees at 2800-3000 RPM (sticker stating this is on top the vanity cover on the spark arestor). you can bump your base timing to 8 degrees.

already covered the fact that the carb is smaller than the Holley 715 CFM carb that came on the motor originally.

however improperly set carb would limit fuel to the motor. is your float level proper?

do you get full throttle travel of the carb? with motor off, move the throttle forward until it hits the stops. then look at the throttle plates. the fact that you have an edelbrock carb were the holley was most likely you do not have full travel as the carb throttle arms are different lengths. you can adjust the throw of the throttle cable at the helm control by putting the cable in another hole

unless someone swapped the drive, its not the drive. the AQ271C was only paired with the 290DPA

 

[Lou C]

Antisiphon valve on the fuel tank can cause this; had the same problem on my boat a long time ago....

 

[kenny nunez]

There is one other thing to check. With the #1 @ tdc make sure that the mark on the balancer lines up with the ”0” mark on the flag with the degree marks. It is pretty rare but the outer ring of the balancers have been known to slip.

 

[Sam Jenkins]

Seemingly all sorted after a little run out this morning. I took the carb off yesterday and blew it out with an airline and also found a small kink in one of the fuel hoses possible cause