350 swap problems

[Tieftoener]

Hello all,

I have a 1988 Bayliner 1950 Capri.
It came with a 305 and OMC Cobra drive.
Due to some crud blocking the winterizing removable plugs, the block cracked in 2005.
I got hold of a free short block 350 from a friend (works at a dealer, was a warranty pull from a 1999 1500 series pickup. The warranty recall was due to failed bearings. The motor only had 20k miles on it. Don't ask me why so few, but it checked out after tearing down the motor.

So, I had it cleaned at a shop. Put all new bearings in it. New push-rods. Left the existing roller truck cam in it. Used existing lifters (cleaned). New rings. New roller timing chain and cover. Used the 350 balancer.

Got a set of Vortec #906 heads on eBay. Cleaned, new parts. New Comp-Cams springs.

Got an HEI ignition. New Holley marine electric fuel pump (for carbs, not EFI).

Picked up a 1410 Edelbrock marine carb on eBay. The guy I bought it from was trying to use it on a 305... just way too much carb. He had swapped out the jets. I drilled them out to be back to the stock sizes (that come with the 1410).

I finally got all this together and working this year. After a few "maiden voyage issues," it's to the point where I've exhausted my know-how and need some advice.

The good:
Out of the hole performance is great (although I'm careful as I don't want to rip apart the boat due to too much engine power).

For the record, I AM aware of this issue as Bayliners are not well known for build quality... and I'm aware of the limits of the OMC Cobra. I'm "taking it easy." The only reason I have a 350 is that it was free and cheaper than a new 305 motor.

The problem:
After planing off, the motor starts to loose power... die... sputter... at around 3000rpm. If I goose it a little on the throttle on plane, it accelerates a little and then starts to sputter and then (without moving the throttle) the RPMs just start going down (slowly) to about 2500. If I pull back the throttle I can run it normally at low RPM.

It's frustrating because I can barely get to 25-30mph for reliable skiing and tubing. And certainly can't "hold" that speed around a corner.

The redline (from what I've read) is 4500 for the Cobra. So, I'm not intending on going any higher than that.

I've searched here and across the web for generic problem I'm having, but have had no luck. The only suggestions I've found are:
- coil replacement
- plug wire replacement
- valve spring replacement (due to floating valves)

I don't believe any of these are my problem as everything listed here is new.

I welcome any suggestions, and thank everyone in advance for your help.

Warm Regards,
Scott

 

[TilliamWe]

Re: 350 swap problems

Fuel issue, I'll bet

 

[searay3]

Re: 350 swap problems

Plumb in a remote tank to the suction side of the fuel pump. There are a multitude of things that can cause fuel starvation. This will tell you if it's the tank side or carb side. (junk in the tank, fuel pickup tube, anti-siphon valve, FUEL/WATER filters, etc). There is also a fuel system troubleshooting guide in the adults only sticky at the top of the forum.

 

[Rat Capri]

Re: 350 swap problems

what type of HEI ?

 

[Bondo]

Re: 350 swap problems

Ayuh,... It's going Lean under load at rpms,... Could be Fuel delivery or Carb tuning...

 

[rs2k]

Re: 350 swap problems

It sounds like a carb tuning issue. When you pump the throttle you get a burst of gasoline from the accelerator pump. That wouldn't happen if the fuel was not being delivered to the carb. At least it didn't work that way when my fuel filters had clogging issues.

I don't think you'll have power problems with the OMC cobra with a Vortec 350.

A stock 1999 Vortec 350 makes 255 @ 4,600 rpm, but I don't think the 1999 Chevy 1500 had them. They started using the 5.3 engine in 1999 on the 1500's.

 

[Honest Don]

Re: 350 swap problems

Not sure how to tune the edelbrock carbs, but i"m almost certain you have a fuel level issue in the bowl or jetting. The accelerator circuit quirts extra fuel when it's called on but when it's gone, there isn't enough. I'm gonna say fuel issue. And how did you accurately drill jets anyway? They have to be spot on and accurate or else you could end up with some issues... like this! Be careful too. If you go too lean at too high and rpm, you could burn a piston. A rebuild should be around $100, might be money well spent.

 

[Tieftoener]

Re: 350 swap problems

Awesome - thanks to all for your responses. I was a little disappointed yesterday as I didn't get any notifications of responses on the thread. Guess I'll have to check the subscription setting and perhaps my SPAM filter.

Plumb in a remote tank to the suction side of the fuel pump. There are a multitude of things that can cause fuel starvation. This will tell you if it's the tank side or carb side. (junk in the tank, fuel pickup tube, anti-siphon valve, FUEL/WATER filters, etc). There is also a fuel system troubleshooting guide in the adults only sticky at the top of the forum.

I took the flame arrester off (I know, I know...) to watch things with a couple friends last weekend.

The fuel is chugging right along. I'm not saying I have calibrated eyes or anything. But, it came out the accelerator pump when it was supposed to.

The 2 main barrels were just gushing the fuel in there.

Just before the secondaries kick in (mechanical), the engine starts to die. And even when they do, it continues to die even more.

Since the metering valves are closing off the primary jets at high rpm/vacuum, I suppose they're closing them off too much?

Thanks for the suggestion on a secondary tank. I'll try plumbing one this weekend. FYI, the filter/water separator is new.

what type of HEI ?

A Chinese Mallory knock-off, 65kV coil, billet aluminum shaft, much like this I found on eBay:
http://cgi.ebay.com/ebaymotors/SBC-...ptZMotorsQ5fCarQ5fTruckQ5fPartsQ5fAccessories

Ayuh,... It's going Lean under load at rpms,... Could be Fuel delivery or Carb tuning...

That's interesting - the "under load" part. If I rev it in neutral and it goes to high RPM's, that would indicate that its getting spark then, right? Thus eliminating ignition problem?

It sounds like a carb tuning issue. When you pump the throttle you get a burst of gasoline from the accelerator pump. That wouldn't happen if the fuel was not being delivered to the carb. At least it didn't work that way when my fuel filters had clogging issues.

Yup, accelerator pump is working (based on my limited understanding). I tried all three settings on the linkage and it didn't any change the results much during takeoff. I think I'm back to the middle setting.

I don't think you'll have power problems with the OMC cobra with a Vortec 350.

A stock 1999 Vortec 350 makes 255 @ 4,600 rpm, but I don't think the 1999 Chevy 1500 had them. They started using the 5.3 engine in 1999 on the 1500's.

Supposedly, the 906 heads were better flow. And with higher flow intake, better carb, roller rockers, its SUPPOSEDLY putting out around 315-330HP. That's just what I've read and correlated with all the research I did on the parts I chose - it's NOT been dyno'd - and honestly, I don't much care. I just want the boat to run like its supposed to

I CAN say its noticeably more than the 230HP from the 305 it had stock. But, like I said, power was not my goal... a good price-to-performance ratio was.

Not sure how to tune the edelbrock carbs, but i"m almost certain you have a fuel level issue in the bowl or jetting. The accelerator circuit quirts extra fuel when it's called on but when it's gone, there isn't enough. I'm gonna say fuel issue. And how did you accurately drill jets anyway? They have to be spot on and accurate or else you could end up with some issues... like this! Be careful too. If you go too lean at too high and rpm, you could burn a piston. A rebuild should be around $100, might be money well spent.

Based on the diameters listed in the Edelbrock carb manual, I associated those to machinist drill bit sizes. And then just drilled out the jets. The primary jets ended up being #33, while the secondaries to #36.

As I mentioned above, the fuel is pouring through the primary venturies in seemingly unrestricted.

I was told that the 750 CFM (model 1410) carb would be a good match for my engine. If it's a matter of rejetting, I'm happy to purchase a jet kit from Edelbrock and try to step them up.

Per Edelbrock, the stock jets are:
Primary .113, Secondary .107

I drilled to:
Primaries: #33 bit = 0.1130" (was approximately 0.1015")
Secondaries: #36 bit = 0.1065" (was approximately 0.0980")

Per Edelbrock, the stock rods are:
Metering Rods - .071 x .047
I have no idea what's in there. Didn't measure them. I probably should (awe shucks)... Come to think of it, I think the guy I bought the carb from gave me another set of rods. Hmmm. Time to dig in the closet.

I'm not sure about the springs for the rods. I assume they're stock, and I don't see optional parts to swap out in the manuals.

I'll be back up where I store the boat tomorrow. I'll measure the rods with a caliper when I get up there and let everyone know.

Thanks again to all for your help!

 

[rs2k]

Re: 350 swap problems

It wouldn't hurt to get the correct rods and jets new to make sure you have the right parts.

A 750 CFM carb is really too big for that engine, but it should work just fine because of the air doors on the secondaries. At 100% VE that engine only needs 455 CFM at 4500 RPM. That engine most likely has a VE in the low 80's which means it should never ask for more than 400 CFM which means a 600 CFM carb would be what you would want.

If that engine were in a car and could do 6000 RPM then a 750 CFM carb would work well.

If I remember correctly, the 1410 comes jetted richer than the 1409 which is the 600 CFM marine carb.

 

[Bondo]

Re: 350 swap problems

I'm not sure about the springs for the rods. I assume they're stock, and I don't see optional parts to swap out in the manuals.

Ayuh,... Get a Strip Kit for it,... It comes with Needles, Jets,+ Springs,... Bunches of different 1s....
With the Strip kit, you can tune that carb to run Right, on about Any motor....

 

[Tieftoener]

Re: 350 swap problems

It wouldn't hurt to get the correct rods and jets new to make sure you have the right parts.

A 750 CFM carb is really too big for that engine, but it should work just fine because of the air doors on the secondaries. At 100% VE that engine only needs 455 CFM at 4500 RPM. That engine most likely has a VE in the low 80's which means it should never ask for more than 400 CFM which means a 600 CFM carb would be what you would want.

If that engine were in a car and could do 6000 RPM then a 750 CFM carb would work well.

If I remember correctly, the 1410 comes jetted richer than the 1409 which is the 600 CFM marine carb.

Thanks very much for the practical information. <sigh> I was initially intending on getting the 600cfm (1409), but several loyal Chevy friends instructed me that the 750cfm is better suited for a "good flowing 350." And, of course, I got a great deal on it (I think I paid $45).

So, yeah, I guess if I had this in rebuild in a truck, the 750cfm would've been a better fit. I will definitely keep this in mind for the possibility of getting a smaller carb later on.

Thanks!

 

[Tieftoener]

Re: 350 swap problems

Ayuh,... Get a Strip Kit for it,... It comes with Needles, Jets,+ Springs,... Bunches of different 1s....
With the Strip kit, you can tune that carb to run Right, on about Any motor....

Pardon my ignorance, but I'm not familiar with the term "strip kit." After doing some more searching this afternoon, I was planning on getting this from Edelbrock:
(Calibration Kit for #1407, #1410, #1412 and #1413)..........Part# 1480
See here:
http://edelbrock.com/automotive_new/mc/carbs_acc/access_calibrate.shtml

Says it has different rods, jets, and springs... so I think we're on the same page.

Based on the #1407/#1410 reference chart (Page 13)...
http://www.edelbrock.com/automotive_new/mc/carbs_acc/pdf/carb_owners_manual.pdf
... what reference number would you folks recommend I tune it to? Of course, I'll try the stock one first. I'm guessing the guy I bought it from had it over somewhere by #5.

Also, in reading the manual, I was wondering if I might have a clogged auxiliary fuel tube. The "transition period" is where I seem to be running out of fuel (based on watching things last weekend). I'll check over things, armed with carb cleaner, tomorrow.

Thanks again for your help!

 

[Maclin]

Re: 350 swap problems

"....Since the metering valves are closing off the primary jets at high rpm/vacuum, I suppose they're closing them off too much?...."

The metering rods will not move down into the primary jets at high rpm, only under light load high vacuum conditions.


Not sure what you mean by "the fuel is pouring through the primary venturies in seemingly unrestricted" You should not be able to see fuel gushing out there while cruising, the fuel will be atomized and be so fine a spray you will not be able to see it except for a fog maybe.

When you drilled out the jets you probably made the mix way too rich. Usually putting in smaller metering rods or stepped rods will be a better thing to do than drilling out jets.

It also sounds like to me the carb secondaries are not getting fuel, which seems almost impossible, or those jets are completely obstructed. Or, there is no air door over the secondaries to smooth the transition. Or the weights on the air door have been messed with.

 

[Bondo]

Re: 350 swap problems

So, yeah, I guess if I had this in rebuild in a truck, the 750cfm would've been a better fit. I will definitely keep this in mind for the possibility of getting a smaller carb later on.

Ayuh,... Actually,... The 750 is a Much Better Fit on a BBC,... Instead of a SBC...
Do the Math,... SBCs can't breathe that much without spinning to the stratosphere....

 

[Tieftoener]

Re: 350 swap problems

"....Since the metering valves are closing off the primary jets at high rpm/vacuum, I suppose they're closing them off too much?...."

The metering rods will not move down into the primary jets at high rpm, only under light load high vacuum conditions.

Yes - thanks. I was confused. I thought the vacuum was pulling them down during high RPM. I noticed that I was confused in reading through the Edelbrock manual earlier. I hope this doesn't confuse others following the post.

Not sure what you mean by "the fuel is pouring through the primary venturies in seemingly unrestricted" You should not be able to see fuel gushing out there while cruising, the fuel will be atomized and be so fine a spray you will not be able to see it except for a fog maybe.

It's certainly a "spray"... but its plenty visible enough to me. Does this mean I'm getting way too much fuel?

When you drilled out the jets you probably made the mix way too rich. Usually putting in smaller metering rods or stepped rods will be a better thing to do than drilling out jets.

I wasn't intending to drill them huge. I just wanted to get it back to "stock" for the carb. I knew the previous owner had put smaller jets in as he was trying to run it on a 305 (yikes!). By no means am I implying I am smarter by implying that the "stock" configuration for the carb is well suited to my application. I'm just trying to explain my train of thought. It seems with the information posted here that the 750cfm is indeed too much for my application.

It also sounds like to me the carb secondaries are not getting fuel, which seems almost impossible, or those jets are completely obstructed. Or, there is no air door over the secondaries to smooth the transition. Or the weights on the air door have been messed with.

The "air door" is there, if by that you mean the "air valve" as referred to by Edelbrock.

They (the secondaries) do get fuel mixing into the venturis if I open the throttle far enough. Sorry if I wasn't clear on that. The problem is that the engine bogs down just before that.

I was trying to say that during the transition stage (per the carb manual), there are "secondary auxiliary fuel tubes" that channel fuel through a small inlet BELOW the secondary venturis. I don't remember seeing any fuel coming in the secondaries until I saw it through the secondary nozzles that mix in the secondary venturis as the air valve opens. Thus, I thought that perhaps the auxiliary nozzles might be gummed up/clogged. On the other hand it'd be rather hard to see since the auxiliary nozzle opening is right at the same level as the edge of the air valve in its closed position.

For those that may not know, the purpose of the secondary auxiliary fuel tubes is to provide fuel in the transition stage just before the fuel starts mixing through the secondary nozzle/venturi. This is the stage just before the weighted secondary air valves start to open.

Is there a way to tell if the weights have been changed on the air valve? I'll inspect them carefully to see if I can find any obvious signs of tampering. Are the weights changeable? Thus far, I haven't found kits to do this... but that doesn't mean they don't exist...