'95 330DA 7.4 engine hesitation issue

LMBoat

LMBoat

Well-Known Member
Oct 4, 2006
757
Ft Lauderdale
Boat Info
1999 450 EB
Engines
Cummins 6CTA's
To All,

Could use your help. Here's the specifics: 1995 330 DA w/twin 7.4s, carbs, V-drives, closed cooling, and 1,600 hours. Engines run great, compression good, no issues except:

Sometimes, after running on plane, then a shut down to anchor, when I throttle up to leave, the strb engine will hesitate for a few seconds while trying to get on plane. Once the boat gets on plane, no issues. It does not happen all the time and therefore has been hard to diagnose. I have changed fuel filters, checked fuel lines, treated the fuel, etc, but it still happens. A few weeks ago, I changed out the distributor pick-up <had a similar problem on an engine years ago and this fixed the problem>. I thought this had fixed the problem, but it happened again last weekend.

It is not a tranny/prop problem, nor is it from bouncing the prop in the sand during take off. It does not seem to be dependant on fuel level in the tank. Guages are all good <no overheat, low oil pressure, etc> It seems like a vapor lock problem. Fuel pump is relatively new. coil? ignition amplifer?....The plug wires are relatively new. It is time for a new dist cap and rotor however. The only thing I have not done it to peer down the throat of the carb to confirm a fuel issue vs ignigition, but that's dangerous, and again the problem happens sporadically. Any other ideas on whatelse to check?
 
When you accelerate do you ease into the throttle or do you open the throttles rapidly? It could be the accelerator pump on your carb - either it needs to be adjustment or could need a rebuild. The purpose is to provide an additional measured amount of fuel into the primaries when you accelerate to avoid the hesitation or 'bog'.

You can easily check - get to a point with the engine off where you can see down the carburetor. Look at the carb and have someone else advance the throttle - you should see a squirt of gas every time the throttle is advanced. If you don't see the squirt then you most likely need a rebuild or good cleaning. You can always compare the results with the other engine to see how things look. Just carb spray wont do it - it needs to be taken apart and really cleaned - while you are at it and have it all apart you might as well replace the other gaskets, etc and rebuild the pump itself. If you see a squirt but it's not much, most of the linkages have 3 positions - and the default is typically in the middle. Changing the hole where the linkage goes to is what adjusts the 'throw' of the accelerator pump itself.
 
I'm easy with the throttles while getting on plane. I'll push them slowly up to about 3,000 rpm to get going. As the rpms increase, at about 2800, that engine will drop 800 or so rpm for just a few seconds. You can feel it as well as see it on the tach. If I just leave things alone, it will go back to normall, drop one or two more times, then run fine.

The accelerator pump does work at the dock, but that's not necessarily proof it works all the time as the problem does not appear all the time. Thanks for the suggestion.
 
It sounds like a fuel delivery problem. The easiest way to eliminate the carbs is to swap them on the engines and see if the problem moves with them.

It seems that the starboard engine is suffering from fuel starvation-where the fuel bowls are going dry. This is caused by poor fuel pressure, blockage or a sticking float. Swapping carbs would go a long way toward sorting this out.

-John
 
How old is the fuel? How long has the problem been happening? How long were the engines shutdown before you restarted them? How long do the engines operate from start-up until the problem exhibits itself?

WAG? Fuel vapor in the lines or a weak fuel pump. Do you have that goofy fuel / water pump combination?

Best regards,
Frank
 
Swapping carbs is a good idea.

Fuel: Very fresh
The problem has happened a few times each year for 3-4 years
How long shut down: 60-90 mins, after running from one hour to 3 hours.
Engines have been running for 5 mins or so before throttling up
Yes to goofy water/fuel pump combo
 
I agree on a carb swap. You most likely need a carb rebuild....when was this last done?
 
PlayDate said:
It sounds like a fuel delivery problem. The easiest way to eliminate the carbs is to swap them on the engines and see if the problem moves with them.

It seems that the starboard engine is suffering from fuel starvation-where the fuel bowls are going dry. This is caused by poor fuel pressure, blockage or a sticking float. Swapping carbs would go a long way toward sorting this out.

-John
Click to expand...
I concur. Sounds like fuel to me. Swap the carbs and see if the problem follows. If it does-rebuild or replace the faulty carb. Might want to consider doing the other one at the same time as a preventative measure. OTOH-if it isn't broke......
 
I have not rebuilt the carbs in the 6 years we've owned the boat, and I don't believe the previous owner did either. The rebuild kits for these carbs are $200 a pop. Anyone know why they are so expensive? I've never seen a rebuild kit for a carb that was that expensive.
 
LMBoat said:
I have not rebuilt the carbs in the 6 years we've owned the boat, and I don't believe the previous owner did either. The rebuild kits for these carbs are $200 a pop. Anyone know why they are so expensive? I've never seen a rebuild kit for a carb that was that expensive.
Click to expand...

$hit, you can buy a whole carb for $200? That's odd.

Doug
 
LMBoat said:
I have not rebuilt the carbs in the 6 years we've owned the boat, and I don't believe the previous owner did either. The rebuild kits for these carbs are $200 a pop. Anyone know why they are so expensive? I've never seen a rebuild kit for a carb that was that expensive.
Click to expand...

That's nuts! Rochester kits are cheap. Get the tag number off the carb and try a different supplier. Auto parts suppliers are ok. The only parts in the kits are gaskets, needle valves, metering rods and and jets, which are the same between marine and auto. I have a Rochester rebuild kit downstairs. It's still factory sealed. It's up to you to determine applicability.

DELCO part numbers:
CarbKitDelco.jpg

Mercruiser Quicksilver part numbers
CarbKitMerc.jpg


As you can see, the only difference between a merc kit and a GM kit is a parts number sticker. Despite the photo on the box, this is for a Rochester 4bbl. Inner package is unopened.

Best regards,
Frank C
 
Last edited:
I concur on the Rochester's. I had those on my last boat and I think the rebuild kit was about $30. I have Weber's now <97805 SAM 0965 is the carb #>.
 
Sorry to hear that you have webers. Try google?

To those guys who think carb are better, cheaper, and more reliable than EFI... guess not. GM's MEFI units are rock solid. Glad I've got them.

Try
 
Does the 7.4 have Rochester carbs? I have/had Webers on my 4.3LXs - the rebuild kits for those were about $135-165 depending on where I looked. I finally just replaced it with the Edelbrock 1409 which is basically the same carb as the Weber 9600 - it even has Weber stampings on it. The whole carb was only $335 at Jegs.
 
I talked with these folks prior to our carb rebuilds: CliffsHighPerformance.com

I was impressed. From an email chat with them:

"Greg, yes, we rebuild Marine quadrajets. We install bronze shaft bushings, and rebuild them with the best components available, which include an HP needle/seat assembly, ethanol resistant accl pump seal, secondary cam/spring, new fasteners, gaskets, seals, small parts, etc. We also run them on our test engine for 30 minutes to verify the calibration, prior to shippping"
 
Before you even consider rebuilding/replacing them....please swap them so that we can determine if they are the source of the problem.

Also, it isn't a question of if a fuel system (carb, MPI, TPI etc.) system will fail it is when. I see these debates all the time on fuel injection versus carbs and frankly it comes down to maintenance. You have 1600 hours on these engines which means somebody has done a pretty good job of maintaining things.

-John
 
Duh....you're right about my error in the number. It's 9780s 0965 on the tag on the carb.

I agree about the swap before going through all the trouble of a rebuild.

Thanks for all the comments
 
Hello All,

Update on this issue: I did swap carbs last Sept and have not had this problem re-appear <not unusual as this has been a sporadic problem>. I've put about 70 hours on the boat since them. This weekend, the problem happened again to the same strb engine, ruling out a carb issue.

This weekend I swapped over ignigition modules and coils and will see what happens. After that, it will be a fuel pump swap.

Any other ideas?
 
You must log in or register to reply here.

Forum statistics

Threads
113,308
Messages
1,430,410
Members
61,172
Latest member
rgtsilva67
Back
Top