Jetting new Holley ...couple questions

[mikeneal]

I am in the process of replacing the factory 2 barrel Holley carb on my vortex Volvo Penta 5.0GL SBC. It has a 4 barrel spreadbore manifold from factory and I bought anew Holley 4175 spreadbore carb. Volvo Penta uses same basic carb on theier 5.7GL motor. I talked to Holley and set the carb up same as the stock 5.7 carb. (61 main and 2.5 power valve). I sea trailed it tonight and ran it a cruise (easy 3000 RPM) for about 5 minutes and did a plug reading. When I shut it off it It diesels really bad, not a good sign. Any I checked #1 and #7 and both were pure white, way too lean. So I idled back to dock and pulled carb apart. My question why is it so lean? I am surprised it is so far off as compared to the 5.7 jetting, I figured it would be closer with the 61s.

Tonight I disassembled the carburetor to make sure all passages were clear (no flashing of debris from the manufacturing. It appeared clear. So I went to size 69 mains and sea trailed it tonight, it is still lean and dieseled slightly after I cruised at 3000 RPM for about 3-4 minutes. Plugs had some slight color (black) where the porcelain was shielded by the ground electrode but the majority was clean white. So I quit before I hurt it (69 was largest jets I had). I am slightly worried I am so far away from the initial setup. (had 61s from Holley). Is 4-5 minutes long enough to color plugs? I sure don't want to hurt it so figure checking early is safer. Once it is jetted properly will it not diesel upon shut down to read plugs? I say this because I never have shut boat down in this manner under normal operation. Should I buy like 80s and make it fat as heck and start way up there?

Please forgive my ignorance, I did a search and learned a ton on here and ordered a couple Holley tuning books from amazon but they are not here yet.

 

[MikDee]

Re: Jetting new Holley ...couple questions

Silly question, You do have a fuel line feeding both fuel bowls right? primary, and secondary. Aside from that I'm clueless.

 

[John_S]

Re: Jetting new Holley ...couple questions

Most I/O's need to idle a minute or two after being on long cruising runs to prevent dieseling. Running on a lean condition will increase cyl temp and probably make it more prone to diesel. But, I would not use diesel yes/no as a tuning guide.

I would have expected the stock settings to be very close, if not right on. If you have re-confirmed that all tuning parts of the carb are set-up the same as a stock vortec volvo, I'd hook a vacuum gauge and verify no leaks, before changing any tuning. You do not want to be compensating for a leak or other engine problem.

At 3000rpm the vacuum secondaries are probably just starting to open. I haven't touched a Holley in many years, but most carbs are jetted via making WOT runs/tests. Even at wot, the sec won't be fully open. All I'm saying is 3k might not be a good place to adjust to. I am sure there are some Holley experts here that will be able to help.

Plug reading is somewhat of an art, especially with reformulated fuels. Some detailed photos for the experts might help.

Unlike double pumper Holley's this carb has single fuel inlet with a transfer tube.

 

[Buttanic]

Re: Jetting new Holley ...couple questions

Might be too much carb for a 305. The carb may not be getting enough venturi vacumm signal to pull the fuel from the bowl because it is too big. I am running a 600cfm Holly square bore with 65 mains on a 5.7. The spread bore is 650 cfm. A Holly 2 barrel is 500 cfm which is more than enough for a 305. I really don't think you will see an improvement in performance and maybe a decrease by being over carbed which is a common mistake people make.

 

[SuperNova]

Re: Jetting new Holley ...couple questions

1.-It is a spreadbore, which means the primary bores are MUCH smaller than an equivalent squarebore and smaller than the bores on your old 500 2bbl, so air flow and venturi vacuum shouldn't be a problem. Unless the boosters are defective.
2.- I think there may be a better way of reading your plugs for accuracy. You can tell whether the plug is running too hot or cold by looking at the end of it and you can spot detonation if you are really knowledgeable, but that is about all you can tell. To truly "read" a plug, you need to look down inside it with a light and maybe a magnifying glass (depends on how good your eyes are). What you are looking for is a brown ring on the ceramic. The closer it is to the end of the ceramic(up) the richer the engine is, and the farther down inside the plug; the leaner it is. If the plug is running too hot, you might not see it at all. My first advice is: You've basically recertified the engine by changing a major component, did you check to see if the 4bbl version of your engine runs a different plug? My second advice is: Go 2 steps colder on your plugs and go back to the 61 jets and 2.5 power valve. Tuning wise, holleys are very close right out of the box and I could see fine tuning for atmospheric conditions or elevation, but not to the extreme you've had to do, unless the carb itself has a fault, but holley is pretty good about quality control. If it's dieseling, it's because it's finding a secondary source of ignition(hot spot) and by going way rich with it you are using the excess fuel as a combustion coolant which is why it's getting better. A boat motor is very easy to tune in that any engine that is running lean tends to surge, but you have to be able to hold the throttle very steady to feel it, and boats are very condusive to holding the throttle very steady. So I believe if it truly was lean, you would feel it surging and maybe even popping back through the carb a little just before the boat got onto plane (high load). So my feeling once again is go with cooler plugs and the original jetting. 'Course I've been wrong before.
--
Stan

 

[John_S]

Re: Jetting new Holley ...couple questions

3 - It has vacuum secondaries which will only open far enough as the engine needs. 100cfm less than the q-jets that were run on these engines up through the 80's.

Given the spreadbore manifold, choices of 4brls was this Holley or a rebuilt Q-jet.

 

[SuperNova]

Re: Jetting new Holley ...couple questions

I agree, john. I just didn't make that point because at 3000 rpm cruise I know my secondary air valves aren't even opening yet and I have a pair of 260hp 350's, so on his 305 it is probably a fair bet they aren't open yet, either. But even if they were, they only open as far as necessary for the air demand of the engine, so that shouldn't be a problem, as you already stated.
--
Stan

 

[MikDee]

Re: Jetting new Holley ...couple questions

Unlike double pumper Holley's this carb has single fuel inlet with a transfer tube.

Aha, Yes, transfer tube, this is what I was refering to, I guess I was thinking double pumper.

IMO, you had done everything right the first time setting it up as close as possible to the stock configuration. I would restore it back to that to begin with. How are the float levels? I know on a Holley they are externally adjustable. I have to say it's been a long time since I've looked at a Holley, but I prefer Carter, or Edelbrock myself, I never had much luck with the few Holleys I've had, but as a spreadbore, it sure beats a Q-jet.

 

[Scaaty]

Re: Jetting new Holley ...couple questions

but I prefer Carter, or Edelbrock myself, I never had much luck with the few Holleys I've had, but as a spreadbore, it sure beats a Q-jet.


Yep..for what its worth, I put a Edelbrock 600cfm with spreadbore (had a Q-Junk orig) adapter, and aint touched it in 3 years..

 

[mikeneal]

Re: Jetting new Holley ...couple questions

I messed with some HP automotive stuff back when I was kid and at least at one time I had a little experience with plug reading, I do agree though it is sorta an art (and not really a great way to judge AF ratio as compared to EGT or an O2 sensor. . Anyhow I have a lighted magnifying reader and am pretty sure the motor is lean. Good call and I did check to make sure the 5.7 used same plugs. Anyhow from the plugs they are hot and it is lean so I scared to run it harder or longer. I am 99% sure that is why it diesels. Anyhow I talked to Holley again and the rear metering plate is equal to a #75 jet. The factory setup for the VP 5.7 is a equal to a #65 jet for rear plate. So I am now 9 sizes larger then factory setup on primary jet and 10 larger on secondary side. Holley guy said no way, there is either something wrong with casting of the body or metering block or a defect of some sort. Has 16 inches of vacuum and idles smooth as glass so I am sure there is no vacuum leak that is leaning it out. I have taken it apart twice looking for trash and it is all clear as far as I can tell. Although it is new, since I bought it from a 3rd party guy no warranty. They said for $125 they will "flow and repair" it. Downside is if it need a goofy part (like a metering block) that is extra, could lots extra (the guy thought they were ~100, body could be 200, yikes we are now over price of anew carb, oh, and 8 week turn around time. Looks like the old 2 barrel is going back on while I scratch my head.

Please keep suggestions coming if anyone has any.

 

[John_S]

Re: Jetting new Holley ...couple questions

OK, a rebuilt with unknown origins may explain things. While not as popular as the Edelbrocks, I have seen a number of people using the marine 4175s on SBC. Most, if not all, were just bolted on and no rejetting required. If the supplier is willing to refund money, consider just starting with new.

I still think it was nice of volvo to use a 4brl manifold on their 2 brl engines. Us merc guys would have had to swap the manifold back, to complete the boating season.

 

[87 bayliner]

Re: Jetting new Holley ...couple questions

did you have any back fire out the carb during your installation tune up process? the backfire will rupture the power valve in the carb causing fuel to pass unchecked possibly leading to deiseling.


j

 

[mikeneal]

Re: Jetting new Holley ...couple questions

It was/is a brand new carb but it came from a 3rd party who bought it from a marine supply that went out of business, so I own it free and clear and with no warranty. It never back fired and a blown power valve will actually cause opposite effect and greatly adds fuel (rich) the mixture.

 

[SuperNova]

Re: Jetting new Holley ...couple questions

Mikedee has a good point about checking the float levels. If the fuel in the bowls is low then the fuel in the main well is low also and will take more vacuum to pull it out. also if the fuel pump cant keep up with the added demands of the bigger carb, that might not help either. And I wouldn't compare the stock jetting on a rochester to try to find the right jetting on a holley. The two carbs work differently and use different systems. Jetting is directly related to airflow with minor variances due to atmospheric conditions and engine efficiency in regards to airflow velocity thru the venturis dictating how strong a vacuum signal is present to pull the fuel out. Actually atmospheric pressure in the bowls is what pushes the fuel out, but let's not pick nits here. The last thing I can think to check right now is to make sure the bowl vents are not obstructed, if they are it will definitely affect fuel flow adversely.
--
Stan

 

[mikeneal]

Re: Jetting new Holley ...couple questions

VP uses the same carb on their 5.7 GL motors. I am/was comparing the jet ## to that. The Holley Tech guy verified I have the same metering block etc. so the jet correlation should jive. One thing I thought about/realized is I think VP uses a thin (~0.50" )spacer under the carb on the 5.7GL that I do not have . Perhaps that is effecting the flow path as the AF enters the manifold from the carb. I am looking around on-line to see if I can buy just that spacer and might try that.

 

[mikeneal]

Re: Jetting new Holley ...couple questions

Update...
I sent the carb back to Holley for their "flow and repair" service, I had convinced myself there was flaw in the metering block or something from manufacturing. I just heard from them and they said they put it on the flow bench and it flows fine, no issues what so ever. Wow, now I am confused , I have the carb back with the flow spec sheet from Holley, sure enough it looks good. S o I got to thinking, I never did the exact same test (3000 rpm cruise and quick shut down plug reading ) with old factory /stock 2 barrel so I did that last night. Guess what, dieseled and the plug was clean white and looked new (was not) . I am really lost. Could it really be too lean and still basically run OK and not blown up by now? Am I an idiot and forgot how to read plugs totally (using lighted magnifier glass). The plugs are stock heat range. I looked at them after I was home and they are dark brown and looks like it does every time I have ever changed them in the past . No-wake zone back to ramp and then flushing (salt water boat) so it has idled a while.
Oh I have not made a fuel pressure test rig yet but it has electric pump and if the fuel flow was an issue wouldn't it show up more at WOT (run bowls dry) ?

Sorry for the long post, please keep ideas coming.

 

[Buttanic]

Re: Jetting new Holley ...couple questions

If it is lean to the point of detonation the sign is tiny, shiny black balls stuck to the insulator. This is aluminum being burnt from the piston top. If it is just barely on the edge of detonation it may not show up on all plugs because of uneven mixture distribution. I have seen it on my circle track race engines. When you tear down the engine the pistons have these tiny craters on the tops. It doesn't seem like you should be lean. Something else could be adding heat to the cylinders to cause the dieseling such as too much timing, over proped or too high a compression ratio for the octane or poor cooling.

 

[mikeneal]

Re: Jetting new Holley ...couple questions

The motor is stock (compression) and timing is per the factory specs. One jet sea trails the boat was actually under propped as I was wakeboarding that day and I under prop it to keep the motor in the sweet spot at slower speeds.

If it is lean to the point of detonation the sign is tiny, shiny black balls stuck to the insulator. This is aluminum being burnt from the piston top. If it is just barely on the edge of detonation it may not show up on all plugs because of uneven mixture distribution. I have seen it on my circle track race engines. When you tear down the engine the pistons have these tiny craters on the tops. It doesn't seem like you should be lean. Something else could be adding heat to the cylinders to cause the dieseling such as too much timing, over proped or too high a compression ratio for the octane or poor cooling.

 

[Buttanic]

Re: Jetting new Holley ...couple questions

If the engine doesen't ping under acceleration (preignition) and it shows no signs of detonation which usually only occures at WOT high load conditions I wouldn't be concerned about the dieseling on after a hot shutdown.

 

[mikeneal]

Re: Jetting new Holley ...couple questions

OK, so the dieseling when I do a plug reading hot shutdown is OK, I noticed if I let it idle for like 20 seconds it does not do it so I am considering that a non-issue. I still don't know why the plugs are so white/lean.