Starts loosing power, gas milage is bad

Axel-Breaker-Earl

MazdaMitch 400 RPM seems dreadfully low so low that I doubt it's getting enough oil everywhere it needs to be.

I have the idle (when warmed up) set at 750 rpm......it is only at 400 or so when it is cold out (30° - 40°) and I have just started it and tapped the gas pedal to disengage the choke. In FL I don't adjust the choke to stay on the fast idle cam any at all (other than startup).......once I tap the gas pedal on my truck, the choke is completely disengaged. I don't let it sit there and idle any amount of time really, and once I get to the end of the street that I live on, the truck is idling around 600 to 700 rpm. I have good heat for the heater shortly thereafter.
The point that I was trying to make is, when the cold engine is idling that low, I can still drive off in it without giving it much gas at all....if I wanted to. That tells me that I have no vacuum leaks with the carb at all.......it is sealed up really good.
Also, I have the Weber choke heater connected to the 7.5V alternator output, or whatever the exact voltage is there, and it works for FL weather on my 2.2 engine it seems.

Red91EFI

Since it came up, here's some feedback on the stock fuel injection used on the B2200. I own a 1991 fuel injected B2200 that's been in the family since new and it's never had a problem. Still runs great with well over 300,000 miles on it. I'm glad it came stock with fuel injection and not that Mazda carb. Here in California we have strict smog control inspections and my truck has always passed them. Good luck passing with a carb.
Don't know how true it is but I've heard that Mazda basically used the Miata fuel injection system on trucks sold in California 1990-93

Axel-Breaker-Earl

Red91EFI Don't know how true it is but I've heard that Mazda basically used the Miata fuel injection system on trucks sold in California 1990-93

I'm not sure what the Miata had on it, but the B2200 EFI is almost exactly like the B2600i fuel injection system. Even the ECM's are very close to each other, when looking at the boards/electronics within them. If the B2200 EFI had been a 12 valve engine, I bet they would have shared throttle bodies/intake and all.
I have several complete EFI systems for the B2200, and one day I will install one into one of my B2200 trucks......I hope!

lizardkingjr

Slightly tangentially on topic: Has anyone ever put a Holley Sniper on a carbureted truck besides SkillBilly Syndicate on YouTube?

MazdaMitch

lizardkingjr I don't think so and I watched his YouTube video about it he put a lot of work into it and in the end he was not happy with it.

Not sure if that would be the case for everyone or just him 🤷🏼

kz6fittycent

lizardkingjr there's another guy here that did and then boosted it. He said the Sniper alone was well worth the money. I guess it depends on the setup and usage.

rev10eight

Axel-Breaker-Earl

No, I though t it was the same. This is what I used. Same stuff Mitch used in his video. Believe I used his amazon link for it.
Just checked with carb cleaner all around it while running, no leak detected that way at the carb plates.

rev10eight

1/28/25 Follow up.

On Fuel Side
I removed the electric pump out of the tank and converted it over to a simple pickup port in place of the unit.
It looks like the illustration picture below. I also changed the old fuel lines out to new lines.
The tank looked pretty clean So I didn't completely drain and blow it out. The bed is not on the truck yet so I can still do it. Any debris I dislodged in the lines came to my glass filter. I can get that cleaned out.

Still giving me problems.

On the fire side
I have replaced:
All 4 new plugs
All sparkplug wires and coil wire.
New spark power coil.
New distributor cap
new rotor/button In the dist
(Possibility that the distributor is not advancing correctly) May replace to find out.

The things I thought of that I am left with to check
Remove vac line to auto transmission and plug, as stated before, yet to do.
Same with the brake booster.
Distributor not advancing/over advancing as it should. May have to replace to find out.
Just looking at Mitch's carb install video. I may want to check the second adapter plate to make sure it hasn't cracked.
Could the dang carb be bad?
I could replace the carb but that's an expensive test.

Far reach
Check valve adjustments, something may be loose or out of adj.
Have compression tested.

Cusser

rev10eight Distributor not advancing/over advancing as it should. May have to replace to find out.

You should be able to test distributor advancing with your timing light, actually see the timing mark "moving".

rev10eight

Thank you. how far should it advance when reving? Stay on 12BTDCH or move up/down?

Cusser

Most internal combustion engines should be about 30 degrees before top dead center at about 3000-3500 rpm.

As the engine rotates faster, the spark must start earlier for combustion at the right moment. "Old VW Guys" know this !

rev10eight

Cusser
Thank you, I will try to check. She starts sputtering at or around that rpm.

rev10eight

I checked the distributor today and it advances the best I can tell. I spoke with carbs unlimited tech and after several adjustments ,changes and tests, it's still doing the same thing. He said the carb is working as it should and ruled that out. He feels there is a vacuum or intake leak somewhere. I have sprayed this thing down with carb cleaner while it was running checking for leaks but as yet have found none. I also want to get one of those EGR plates from mitch to rule that out also.

I did have the truck get hot a few months back before this problem came up. I had a fan relay get stuck in the off position. I fixed that and didn't think anything else about it. the problem started a month or so later so there might be a connection. At this point I'm out of options.

I'm going to check the intake bolts. If that isn't it, I'll pull the carb and intake and make sure its all good. Take it all apart, clean it all good then reinstall the plates, carb and intake all over to certify that it is correct. Maybe I have a blown head gasket but I don't have the normal symptoms. A head gasket ain't that hard to change.

If anyone want to call and talk this over and try to help me out, pm me and I'll shoot you my number.

Cusser

rev10eight reinstall the plates

Confirm that the plates are PERFECTLY flat, or sand them flat on a sheet of glass. See the Tech Section.

rev10eight

Cusser

Pulled and plug vacuum line from brake booster, auto trans and distributor. No change.

Pulled the carb and plates. Inspected intake manifold and also made sure bolts were tight- all good.

Found I had mard the bottom plate with the carb bolt on first install but that was not the problem . Done Both plates on a window I had. Started with 120 finished with 600. I marked all over the plates surface with a magic marker. Once all the marker was gone, I knew I had it flat and smooth. Inspected carb for cracks, all looked good. Reinstalled and guess what? Still have the same problem.

Going to check my fuel pressure tomorrow to make sure my new mechanical pump hasn't started crapping out on me. I'm still suspecting this carb.

kz6fittycent

rev10eight if your plugs are reading good, the question is, was that after a run down the road or was it from just idling? There's a difference because of the different circuits in the carb. A lean fuel mixture can cause backfiring through the carburetor. Adjusting the air/fuel mixture can help, but if the problem persists, it might indicate a deeper issue such as a flat camshaft lobe or a tight valve.

Consider this from a "process of elimination" perspective:

You've already changed basically the entire fuel delivery system
The timing is correct and appears to be advancing
The carb is clean and you've contacted the vendor - the vendor has indicated there's not a problem
You've checked for vacuum leaks and repaired the adapter plates
You stated it starts getting sluggish when the second bbl kicks in and the engine is under load
a. This is what indicates a lean condition IMO. You may need to buy a jet kit and go up a couple sizes and see if there's a change. I had to do this!

rev10eight

kz6fittycent
Thank you

"plugs are reading good, the question is, was that after a run down the road or was it from just idling?

I ran it down the road

There's a difference because of the different circuits in the carb. A lean fuel mixture can cause backfiring through the carburetor. Adjusting the air/fuel mixture can help, but if the problem persists, it might indicate a deeper issue such as a flat camshaft lobe or a tight valve."

I can check the valves but have not did that yet.

Consider this from a "process of elimination" perspective:

You've already changed basically the entire fuel delivery system
The timing is correct and appears to be advancing
The carb is clean and you've contacted the vendor - the vendor has indicated there's not a problem
You've checked for vacuum leaks and repaired the adapter plates
You stated it starts getting sluggish when the second bbl kicks in and the engine is under load
a. This is what indicates a lean condition IMO. You may need to buy a jet kit and go up a couple sizes and see if there's a change. I had to do this!

That's is what we did while testing with the factory tech. We changed main and secondary idle jets and main and secondary jets. Did the bowl jets first and checked, then the idel jets. After doing the jets, we rechecked the timing and best lean air mixture.

Valve adj might be too tight, I'll check that.

The tech said they may have changed the fuel in my area for winter. That's why we uped the jet sized to make up for the lean condition. Ethenol fuel required more fuel volume to compensate for fule burn.

I'm going to drain the last of the tank
And put non ethenol in it. That's what I'm going to run if I ever get it running right again.

When I put the new head on this, I didn't rebuild the lower. It has probably 60k on it. Could be something to consider.

kz6fittycent

rev10eight heat can definitely impact cylinder pressures which would induce lower power, but it's the backfiring that really indicates the main two things I was saying. So, if you know you're jetting is right (and hey, I run e10 here in TX - all I can get really), then that leaves the valve adjustment. The other issue, hopefully not, is that you have a bad cam or valve train components, leading to the backfire and power loss.

rev10eight

Thank you so much for the information. It gives me something to look into.

rev10eight

My mechanic dropped my other vehicle off today as I Had just finished working on the truck. I had just finished checking the fuel pressure and adjusting all the valves to 10 while cold. I had a couple that was a little looser than they should have been. He asked me what was going on and I told him what it was doing and what all I had done. He will come by Monday and check the compression of each cylinder for me. He said he had a newer vehicle doing this and it drove him nuts until he found it. one of the valves was not closing all the way and was causing blow back combustion. its possible. This new head has about 3500 miles on it but it did get hot once. I've checked all I can check. Going to let him take a stab at it.

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