So I've made no changes to the carb and it ran fine on 19psi before but lately I've been getting a lean condition trying to go wot. Give it some more jet seems to enjoy it went up 6 sizes in the front may still need more until I go stand on it. My question is the engine is basically the same since the rebuild except it's all sealed up with o rings and a touch more compression everything else is the same except new turbo header. I'm starting to debate maybe since it's not broken and eating coolant now am I seeing that it needs more fuel on the afr gauge or I'm wondering if the BRPV isn't opening not too sure I may try blocking the PV and note any change? AfR used to be spot on before the changes but now it's climb to 13 or 14 then I get off the throttle. Oh also probably the biggest change is a lot less timing 18 initial and total it's locked now. I ran way to much timing before that's what broke two pistons and a head gasket lol. I'm just curious since it seems I'm jetting up so much I may be making up for a not functioning PV.

Kev

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What is your fuel pressure when this is happening? I had a similar issue, and discovered that my electric fuel pump was not rated to put out above 12 psi even though the my pressure regulator was trying to increase psi above 12 psi. I changed to a different fuel pump and solved the issue.

Brian

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Flyin' Brian

74 Duster, 225, rear-mounted blow through turbo at 12psi boost, street/strip car
"Sixy Beast"

Good idea, Brian. It could be a fuel supply issue of many types. Hard to see that PV should have that much effect unless it is blown, but then you would see crappy idle.

Maybe get a fuel pressure gauge mounted near the carb and look as you are doing a WOT pull.

Hmmm.

Lou

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Home of Slant6-powered fun machines since 1988

I'm starting to suspect it may indeed be a fuel pressure issue my walbro pump is becoming noisy and my fuel pressure has started to bounce up and down a few psi at idle with the rhythm of the pump noise. Mallory regulator is less than a few months old so I'm starting to suspect the pump considering the carb did not seem to react to the extra secondary jetting I've been tinkering with. Changed dirty fuel filter with debris in it but no changes. Took carb apart cleaned and changed the PV just incase it was blown didn't seem to be though so no change there. The pump noise almost sounds like a thumping or rattle but the lines aren't rattling on anything. Problem is during wot I can't see the under hood fuel psi gauge lol. So I may film it via GoPro or move it and I'm going to try 2step in the garage and see if the gauge builds pressure with boost. Oh and Brian this walbro can run up to 60 psi same fuel system as shaker223 basically.
I just remembered when I changed to the EV carb hat I move the boost line from the hat to the charge pipe right before the hat for the fuel pressure regulator. Would that make any difference in signal? I didn't want to drill a hole in my new hat lol

Thanks for any help or ideas!
Kev

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I wouldn't think the change in placement of the boost reference line would be the issue, but you never know.

I highly recommend installing a fuel pressure gauge where you can see it all the time. Spend the time and money on getting a mechanical fuel pressure gauge with a firewall isolator. This would prevent any fuel from entering the interior in case of sensing line rupture or accident.

Another possibility is the pressure regulator starting to act up. Again, seeing the fuel psi in real time would be very helpful.

Another question, do you have a fuel filter before the pump or after it? I run a filter both before the pump, and after it near the carb (fine steel mesh type).

Brian

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Flyin' Brian

74 Duster, 225, rear-mounted blow through turbo at 12psi boost, street/strip car
"Sixy Beast"

I'm going to rig a temporary gauge on the cowl just so I can watch it at wot unless I can get a light under hood for the camera to see the gauge lol. I've been running just a pre filter for years. The sending unit is stock also so I'm thinking that sock could be in terrible shape and the nub out of the tank is only 5/16 so I'm going to change it just to upgrade to the 3/8 and to be sure the in tank filter is new. I sent Charlie a video of the fuel pressure via email maybe I'll put it on YouTube so I can show you guys with a YouTube link the sound and the needle bounce.

Kev

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I had one of those, and don't like it. When there is heat in the engine compartment, the gauge pressure changes. With a hot engine compartment, and "0" fuel pressure, the expansion of the fluid in the isolator, would cause the gauge to read about 3 lbs. If I wanted to use a gauge inside the vehicle, I would consider a high quality electric gauge. I have never used one, so don't know if they have any issues.

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Charrlie_S
65 Valiant 100 2dr post 170 turbo
66 Valiant Signet 170 nitrous
64 Valiant Signet
64 Valiant 4dr 170
64 Valiant 4dr 225

Charrlie,

You bring up a good point. I keep forgetting with my unorthodox turbo mounting that my underhood temps are much different than most turbo applications. Using an electric gauge might be a smarter way to go.

Brian

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Flyin' Brian

74 Duster, 225, rear-mounted blow through turbo at 12psi boost, street/strip car
"Sixy Beast"

did you figure it out?

I haven't had time to put it on the lift get I carved out Saturday morning to work on it so hopefully I have some answers this weekend. I'll keep you guys posted. I'm going down on one knee today literally lol it's time to give my lady a ring so I've been a bit hectic the past couple weeks lol

Kev

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Wow, sounds like an exciting day! Hope you can help each other to be happy and comfortable...

BTW, how fast has your car gone in 1/8th or 1/4? Just curious...

Cheers!
Lou

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Home of Slant6-powered fun machines since 1988

My quickest was an aborted pass when I murdered the head gasket and two pistons lol 8.2 at like 60 something coasting after grabbing 3rd gear. I almost crossed center 3 times from coolant blowing out of the rad cap. So I realized something was wrong when it was spinning hard in 3rd.

I'm nervous but excited should go well though! She's been a good gal putting up with my shananigans haha

Kev

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Here's an update so I decided to the change the pump after it was making a banging noise and the fuel pressure would bounce with the noise even though the voltage was normal. Fuel filter is new, i changed the sending unit also because the line was only 5/16 and fuel gauge wasn't accurate. So now the sending unit is a 3/8 line along with the entire fuel system. Everything works fuel pressure is solid fuel level is accurate. I can two step the car and watch the fuel pressure rise correctly it's adding 1 psi per boost psi like it should in all conditions. I tested the Meth Injection with a hand pump it starts spraying at 5 psi like I set it forever ago 14gph jet. I suspected my hard line vent tube extensions were a little loose so I installed a pair of angle cut vent tubes which caused it to be to lean to drive. Then I added rubber hose vent tube extensions it's back to driving normal but still gets up to the 14's or more during WOT. Oh and changed the BRPV before all this during carb cleaning. At this point I'm convinced it needs more secondary jet even though my jetting is already huge????? 78/108 currently

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I can't go any higher on the primary jetting or else cruise goes too rich so 78 seems to about my limit on keeping good clean drivability. I'm going to drop in some tighter air bleeds as well to see if I can cut down on some of the air in the mixture instead of adding more fuel. Anyone got any ideas or am I pretty much stuck with throwing jet at it until it gets happy during WOT. It wouldn't be so weird if it was a new build but before the rebuild this setup was dialed in. I guess the slight increase in compression and the motor being all sealed up with the o rings now may have changed something?? Also new larger header and less timing.

Thanks, Kev

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Megasquirt?

Note that at some point, increasing jet size will not make it any richer because the metering block will have passages that limit the fuel delivery. 108s sound like you may be there.

Also, reading lean on an O2 sensor can also mean going rich. If the engine starts misfiring due to rich condition, which you usually cannot hear, then the fuel will not be burned and any O2 sensor will start to read lean. I have seen this several times. Try leaning out and see if it starts reading richer. You may be so far past the point that you'll have to come down quite a bit. Of course, if this is wrong and you stay in it, then you'll blow something, so that's my disclaimer.

Happy hunting,
Lou

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Home of Slant6-powered fun machines since 1988