Rochester carb on a 02 4.3 TKS

[Furbird]

Posted this on THT and not really getting much feedback, wanted to get one of you guys' thoughts...

So the boat is back up running, everything is smooth and fine at idle on the ears. When you increase the throttle rapidly, it tries to bust up some (spitting through the carb sound.) It's been many a year since I've had to do anything with a carb as everything else I own (other than the riding mower) is EFI or electric. I figured it was probably something TKS related as I've heard they have some issues, but it appears that the previous owner replaced that with a Rochester 2 jet (I just got the boat in late May.) Obviously, I'm already in the hole as far as knowledge goes being an EFI person but now I've got a switched carb too (which apparently is a good thing looking around here and on other forums.) But my question is how do you tune this? I've read about a vacuum gauge and watching RPM settings and what-not, the "turn the screws all the way in, back out three turns, and start from there" method only to be contradicted with a 1.5 turn method. So confusing. Boat starts, idles, just starts busting up some coming off throttle. Mind you this is on ears, so I'm sure it will be horrific under load so I'd really like to address this before ever heading to the launch. Plus my oldest nephew wants to try wakeboarding so I've got to have a boat that can get up to speed quickly and not baby him up to speed.

If I need to bust out the timing light I have one if anybody thinks it's timing related, but it really sounds like a fuel delivery issue and not a spark problem to me. Temps never even got to 150 on the ears so I wasn't trying to emulate John Force or anything in the yard. I know ears are not the best water source according to many of you guys here and on iboats but I had excellent flow and the water coming from the outlets on the outdrive were no hotter than what comes out of my faucets in the house.

 

[alldodge]

Always want to make sure the timing is correct, with a TB5 it should be 8 BTDC in base timing mode

Was the motor warmed up where the enrichment valve had closed on the carb?

The TKS carb can be adjusted but calls for a special tool and a cover has to be removed to get at it. If the carb does have issues then it needs to come apart.

Most that change from TKS to Merc/Rochester 2bbl are doing it because they have issues warming up and want an electric choke

 

[Furbird]

It doesn't have the TKS carb anymore, it has a Rochester 2 jet. That's the one that's spitting back. Couple of replies have been accelerator pump related and if I have to rebuild it that's fine, but how do you tune it? If it's a tuning issue I'd rather try that first before a complete tear down.

Again, it was originally TKS but the previous owner converted it at some point to Rochester.

 

[alldodge]

OK, thanks my bad

Always want to make sure the timing is correct, with a TB5 it should be 8 BTDC in base timing mode

Correct plugs and gap being used

Once idle speed and timing is correct and verified and if it still does it, then need to get into the carb. May need adjusting, but my need rebuilding and adjusting

 

[Scott06]

I don’t think the TKS was installed as early as 02, my 2004 had and electric choke mercarb. Do you have one idle mixture screw or two?

all dodge has you pointed in the right direction. Might be worth checking contents of fuel filter And 1.5 turn out is the normal starting point for mixture screw.

 

[achris]

.... When you increase the throttle rapidly, it tries to bust up some ....

??? Have NO IDEA what this even means. Can you describe what's happening?

With a non-standard carb, you're going to need to open it up and read all the jet sizes, then check them against similar carbs on similar engines to know if it's in the right area.

Chris.......

 

[Furbird]

OK. So sitting in neutral on ears, you roll on the throttle like you would to speed up. If you gradually increase throttle, no problem. If you snap it/floor it/act like you're going to get a skier up, it pops through the carb. Not backfiring, but like it's running out of fuel (lean condition.) It did backfire once or twice out the exhaust during testing but it mostly acts like it's running out of fuel like you would in a car. Back off the throttle and it will idle fine, then you can gradually increase throttle and it will speed up. Never took it above 3k but my hunch is it would act the same way at higher RPM's too as there simply wouldn't be enough fuel getting in there. I do not know the age of the fuel in it but do know it has Sta-bil in it so probably the best course of action would be drain the tank and start fresh. Still would like to know how you adjust this carb though, as other than idle there's only the two screws below the bowl and I am carb-illiterate. With so little adjustment it can't be that difficult. Surely somebody on here has a Rochester 2 jet on a boat!

 

[achris]

OK. So sitting in neutral on ears, you roll on the throttle like you would to speed up. If you gradually increase throttle, no problem. If you snap it/floor it/act like you're going to get a skier up, it pops through the carb. Not backfiring, but like it's running out of fuel (lean condition.)...

That's a classic accelerator pump problem. It may be that the discharge jets are blocked, or the pump lever is on the wrong setting.

Also, as it's non-standard, check that it's a proper marine carb... (find a number on it and post that, or a photo)...

Chris.......

 

[Furbird]

17056108. 99% sure after doing some searching that's off of a vehicle, which means either I set it on fire or it sets itself on fire. Wonderful. More BS to deal with. So now the question is where to get a carb? Ebay? Looks like a 3-400 hit.

Break Out Another Thousand. I'm officially naming it that now.

 

[alldodge]

Agree, carb is off an older truck

Have not found a Rochester 2bbl on a vortec V6, Only the Merc carb or TKS

Merc would be 3310-807764A1 or old number 806080A2

 

[Scott06]

Only saw the OEM merc carb on Iboats here for like $800

https://flyingfishcarburetors.com/Y38-3Mercruiser.htm. These guys rebuild carbs with or without a core. Mikes carb shop can also rebuild yours

I agree it does look older, but the choke stove housing is black and accelerator pump arm are green like on a mercarb.

 

[Furbird]

Not paying $800 for a stupid carb. If that one you linked will work I'll buy it, but have no core to return so will be taking the hit on that.

The question I have now is if the intake was changed. Does the Mercarb and the Rochester I have share the same intake manifold? Because now we're opening a whole new can of worms if I order the correct carb for this boat (well, minus the TKS garbage) and then it doesn't fit because the intake is wrong.

 

[achris]

17056108. 99% sure after doing some searching that's off of a vehicle, which means either I set it on fire or it sets itself on fire. Wonderful. More BS to deal with. So now the question is where to get a carb? Ebay? Looks like a 3-400 hit.

Break Out Another Thousand. I'm officially naming it that now.

Yep, that's a boat bomb... Those carbs are 'externally ventilated' which means petrol vapour from the float chamber is vented to the outside world, not internally like a marine carb. Vapour from the float chamber is slowly filling you bilge. The smallest spark and it'll go off. :boom:

Not paying $800 for a stupid carb. If that one you linked will work I'll buy it, but have no core to return so will be taking the hit on that.

The question I have now is if the intake was changed. Does the Mercarb and the Rochester I have share the same intake manifold? Because now we're opening a whole new can of worms if I order the correct carb for this boat (well, minus the TKS garbage) and then it doesn't fit because the intake is wrong.

Mercarb and Rochester 2 bbl fit on the same manifold...

Now, given the carb is non-marine, check everything else. Starter motor, alternator, distributor, and breakers and fuses, the fuel pump. Anything non-marine in those parts can mean... :boom:

Chris....

 

[Furbird]

According to that chart the TKS didn't come out until 05 but I could have sworn I read somewhere than 02 VIP boats had TKS? Good grief this is so aggravating. If I had any hair I'd pull it out.

 

[achris]

... but I could have sworn I read somewhere than 02 VIP boats had TKS? ...

Not VIP boats, Mercruiser engines. The boat manufacturer is not the engine manufacturer. Boat builders buy in their engine, unlike car manufacturer where a Ford car has a Ford engine and a Toyota car has a Toyota engine (except mine :facepalm... Boat manufacturer buy their inboard engines from Mercruiser or Volvo (who buy THEIR base engines from GM. Yeah, it's confusing)... Your engine is the same as a thousand others, in completely different boats, and they'll be dozens of '02 VIP' boats out there with a Volvo engine, or an outboard, or a V8, or inline 4....

That's why we care not about the boat, but ask for engine: year, model and serial number...

Chris...

 

[Furbird]

Fuel pump is the one that mounts vertically on the starboard head. Pretty sure only way you can get that is marine.
Alternator is black, not entirely sure how to check that but will google it.
Stuck the bore scope down to look at the starter before to make sure, it's marine.
Distributor... no clue.
The only fuse I know of in the engine bay is the one on the trim solenoids. It's a glass fuse in a completely sealed rubberized fuse holder. The only breakers I know of are on the trolling motors and they are most assuredly not marine. All the other fuses are underneath the console.

I guess I'll email those guys in the link above and figure out how to proceed. That Y-38-3 is going to be an issue as my fuel pump attaches at the front of the carb currently and that one attaches at the side. That's a hard line so that's going to take some, um, "coersion" to make it line up.

 

[achris]

I think the original fuel line from Merc is a side entry. Post your engine serial number and we can look it up...

Chris.......

 

[achris]

Here's the right carb for your engine...

https://www.ebay.com/itm/MARINE-RBL...448087&hash=item468b3c95b7:g:XwQAAOSwMg5cBtH9

Chris.......

 

[Furbird]

Well, I can't post the serial number. The original engine was an 02, it was replaced with an 01 out of a Chevrolet Express van.

 

[nola mike]

17056108. 99% sure after doing some searching that's off of a vehicle, which means either I set it on fire or it sets itself on fire. Wonderful. More BS to deal with. So now the question is where to get a carb? Ebay? Looks like a 3-400 hit.

Break Out Another Thousand. I'm officially naming it that now.

At this point you might as well upgrade to a 4bbl carb and intake...More choices for both with the vortec than having to go OEM and you'll get yourself another 20+ hp.