Offy Manifold and Holley 390 Carb problems?

Okay along with some other issues working on, the 390 I am running on my new Offy Intake is running very rich on the passenger side.

I have talked with Holley and a few other people, and 1 other person seems to be having the exact same problem. Anyone else using a simalar set up having a simalar problem?

Holley is saying I should not need to change the mixture screws on the passenger side, but It's about all I can at this point.

Dave

 

Any chance that you have a "heat riser valve" where the passenger side exhaust manifold meets the exhaust pipe connection? If so ,check it to see that it opens fully upon warm up or if you dont need it wire it open or remove it.This may or may not resolve the problem but sure is worth checking out.

 

I don't have a heat riser valve installed. Allthough I do have one in my spare parts when I bought the Jeep.

SInce it was never insatlled previously, I didnt think I needed it now.

Should this be connected?

Dave

 

I dont think that it would be necessary,I was thinking that if you had one and it was not opening all the way that it could have restricted the exhaust flow simulating the rich condition on that bank of cylinders. Well, at least that has been ruled out.

 

Maybe change the mixture screws from side to side and see if the problems moves to the other side. You could also open up the carb to check that the jets (orifices) are the same on both sides.

 

Right, you can screw the idle mixture screws all the way out and inspect them. Is this a new or used carburetor? Have you had the carb apart? These carburetors are very simple to dis/reassemble. Take the bowl off and look at the number on the main jets - they should be the same. Note that the idle mixture screws only affect the idle mixture - above idle, the main jets control the mixture. If you have not already, I'd get the kit for the carb and squirt out all the passages with carb cleaner and put it together with new gaskets etc.

 

The Carb is new.

Jets are all clean and in perfect condition. The jets are all the ame #51.

Holley is wanting me to stagger the Jets, and keep my mixture screws set equal side to side.

Whats driving me crazy is whey I should need to stager Jets, unless its something inherit in the dual plane offey and these carbs.

I am going to bump the passenger side Jets down to 49 instead of 51 and see what that does.

 

This carb and manifold combo has been used many times before with sucuss.I believe that the 390 is about top CFM for this motor(a 225 right?) in a Jeep( personal opinion). Seems like you have a problem with this "particular installation". While investigating, change only one variable at at time, such as the jets , so you can plot your results with each individual change.Just for the record,how have you determined that the passenger side is running rich?(no disrespect intended)

 

Okay we have checked and double checked the jets, and the idle mixture screws, float etc.

The onlything we havent done so far is actually flip the carb around to verify that it is the carb and not the manifold. Holley wants me to do that and it is on the list along with staggering of Jets.

As the determination of rich.

I am running dual exhaust, the passenger side exhaust is wet and does backfire on occasion.
The passenger side plugs display unburnt fuel
Temp reading on the carb shows passenger side remains 80-125 degrees cooler during idle and after warm up.

Now my 225 is slightly modified. Comp Cam, bored 40 over but everything on the engine has tested out perfect, we even double checked lifter performance.

Holley has told me to send the carb back and they will verify everything is correct in it and I may take that route, but at the same time there is a member on Jeepster boards that just did the same upgrade Offey with 390 carb and he is having the same problems, passenger side is rich.

 

Well, you have been very thorough in your evaluation. Without any other clues I would have to agree that there is a carb problem. Being that the 390 is a square flange you could rotate it 180 degrees as Holly suggested although it would be a little diffiicult to operate the throttle at a position other then at idle/no load without fabricating a temporary linkage. If I were you I would either do the rotation or swap the main jets from side to side. Keep us posted about this, I am eager to learn what is going on.
Where are you located at?

 

I thought about just swapping driver and passenger side Jets insetad of flipping it 180. Like you said, flipping it 180 won't help me under load unless I fabbed a temp cable bracket.

One thing I am curious about is Backpressure with the Dual plain manifold from offey. SInce the 225 was a stock single exhaust. I did a swap on my exhaust with some different free flow mufflers, not too much more pressure but a little bit. And although I am still running rich and temps still register about the same, there is less "Backfires" and the exhaust seems to be not as wet.

Last night I decided my weekend project is to flip the carb 180 and or swap the jets around and see what happens. Put a more restricting muffler on it. and I purchased 2 49 and 48 Jets to stagger the Jets if needed.

Hopefully I will have some good insight this weekend. If I had another Carb, I would send this back to Holley to have them check it out, but I have a problem believing that the Carb has a problem.

 

Are you sure your distributor is not installed 180 degrees out? That could cause the symptoms you describe.

 

Don't suppose your old carb will fit that manifold. If it does then stick it on and see if you are still running wet on the passenger side. If you are then maybe you have a pooling problem.

As for 180º degrees on the carb, wouldn't a longer temp throttle cable take care of that problem?

 

I'm running a holley 470 truck avenger 4 barrel with an offy intake, cam and header on my 258 without issue.

 

I have done some tweaking to the carb. Reset the timing and increased backflow by reducing the size of the exhaust, I still havent changed to a new muffler, The PO was using Glasspacks basically instead of a muffler.

The biggest improvement on mixture came when I increased Backpressure from reducing the exhaust. I know in a lot of circumstances too much flow is unhealthy, I just never imagined that with a 225 even with my mild upgrades that it could make suchs a difference.

My next plan is to actually add mufflers and remove the old glasspacks, I am thinking about adding a y-pipe and making this a single exhaust as well vs the dual its running now. Holley from the begining was concerned about the exhaust more with differnt lengths from side to side.

The carb is still running slightly rich on the passenger side, but now backfires have ceased, pipe is not wet, the only signs of rich mixture is from unburnt fuel on plugs (very slight) and temp reading difference on carb at idle and after warm up. But the temp has dropped closer to 30-60 degrees off.

The PO had 2 1/4 pipe running back I have dropped down to the orginal 1 3/4 but still dual. After I finsih the front axle work im going to change the glass packs for real mufflers and see what the final assesment is.

 

What are you running for PCV? On my Truck Avenger (4150 style), the PCV attaches to a port on the throttle plate. If you flip the carb over, you see the the venting is straight to the pass side primary throttle bore. This could essentially could be a massive "vacuum leak" for you, possibly effecting your pass side fuel/air mixture.

 

Thought I would update this a bit, SInce I am back and forth between Jeepster club and here.

I reran the exhaust to a Single flow set up 2" pipe with a decent street muffler and a Y pipe this got my back pressure where I needed to be. We measured and set mixture and low and behold She ran like a champ! Idle smooth and through the geras I got great resposne.

Until....

I hit load 3rd gear over 65" after engine warm up. Then I got hit with massivie spitting, and power loss. Checked the plugs and came up VERY lean. Tweaked the idle mixture screws and also increased Jet size from 51's to 54's still lean, not as much but major bogging and spitting has decreased but still there.

This weekend I puled the carb off wnet over it real good cleaned it rejetted back to 53's put it back on and tested vacuum at idle. Im showing 21", now all the tests before where done and my buddies shop using his vacuum gauge, so now I am wondering if he has a faulty gauge, or is my gauge faulty who knows.

BAsed on 21" of Vacuum my powervalve is way to small, 6.5 on the stock 390, aty 21" I would need a 10.5.

Now 21" of idel Vac seems high to me. But the engine is built, mini port and polish, Mild Cam bored 50 over etc etc.

I also think I might have a fuel flow problem, I am showing 6psi of pressure, but flow is different. Im going to step up to a 10.5 power Valve and see what response I get, before I replace the Fuel pump and add a electric secondary pump. The fuel pump on there is new, but I wonder if there is a chance since it is mechanical that delivery at load might not be sufficient.? Clue less at this. Float is always full, but kinda hard to check empty float at spitting by shutting it off on a mechanical fuel pump.

Never ending story of a Jeepster Im also going to hot wire the HEI, just to make sure I do not have an ignition problem, seems I do have some corrded wiring, and I am reading 12V to the HEI, but wonder if theres anydrop at engine temp under load.

Let me know if you have any other suggestions.

Dave

 

I used to run an Olds at the strip and had a similar problem. Great acceleration in first gear but when it hit second it simply ran out of fuel. That was with the headers uncapped. With the mufflers on it was OK.

I added an electric fuel pump and solved the problem. You may be right about a fuel flow problem.

Dave

 

Give you a heads up...

After all the nightmare and everything I fought with on this thing....

The Carb had a flow problem, Speed shop didnt tell me exactly what it was but I took it to them to put on the Dyno and tune, and they knew something was up right away.

They had another 390 in the shop they pulled and put my needle and seat in as well as the 53 Jets and had it tuned in 30 minutes perfectly.

They are going to Warrenty the carb with Holley for me, but it now runs like a champ.

Now its on to the rest of the mods