I'm looking for comprehensive tuning instructions for my 2150. I have disassembled, thoroughly cleaned, and reinstalled a Walker carb kit for the 2150 on my 400. It will start and run but doesn't always want to idle. Seems to idle better when warm. When cold it wants to die unless I am into the gas. Runs fine down the road. Idle mix screws are 2.5 turns out. Float is adjusted per spec (7/16"). The choke adjustments were confusing in the carb kit instructions and so I'm unsure if I have that set right. I've looked at numerous youtube videos and can't figure it out.


Thanks in advance.

 

Welcome to FTE btw.

Sounds like you're doing things right. Carb tuning starts with the fuel tank. A big problem is old tanks full of junk and sediment and varnish, old gas etc. The key is making sure the steel lines are clear and the carb is supplied with the volume and pressure spec at all times under all conditions. Check fuel pump for correct pressure (around 5 psi say) and at least a pint in 30 seconds. If this is not correct it will never tune, starved for fuel, flooding etc. Once you know for a fact fuel delivery is correct pay particular attention to float height - and measure the fuel height in the bowl for spec. Everything downstream from idle to wide open throttle and everything in between is predicated on the correct fuel height in the bowl reservoir at all times.

This 2.5 turns out business is just a mechanical zero or bench setting just so the engine will start and idle. Then from there you can start tuning. From reading the posts here over the years this is a common misconception, it's not the end point. It may run "OK" but will likely be absolutely pig rich. When everything is setup right, just a hair turn of the mixture screws will make a big difference in how it runs, especially off idle hesitation. The idea generally is to lean it out as far as possible while maintaining a smooth idle.

A mechanics vacuum gauge is really useful for engine diagnostics and tuning, and setting carburetor mixtures, can't recommend them enough. Less than $20 and worth every penny.

Mikes carburetors has all the manuals in .pdf for free download. There is a lot of information available for the 2100 and 2150 out there on other sites too. They are excellent carburetors. Their Achilles heel is when they are well worn, high mileage, the throttle shaft will start to wear and waller out the mounting holes in the carb housing and cause a vacuum leak. The fix is to ream out the holes and install bushings. Check for this. One way to test is pack grease around the holes, but basically there should be no sideplay in the throttle shaft.

http://www.carburetor-parts.com/free...ls_ep_274.html

 

Also....FYI- the idle mix screws should be in the neighborhood of 1.5 turns out.........

 

Right - just to get started... On my '64 with stock 2100 both screws end up at 1/2 turn out for maximum vacuum and best idle. Basically any idle mixture screw is there just when the idle RPM starts to drop off.

 

Thanks guys. I did find an awesome manual that verified I did the carb clean and rebuild right. My problem (for now) is the fuel tank. It was full of sediment and needs to be steamed. And for $20, I just replaced the stock fuel pump.

 

So I got the truck running, albeit not very well. Got it up to operating temperature, turned off and removed the air horn to measure the float height with fuel. It was right on at 7/16". I hooked everything back up and noticed that when its running, fuel is pouring out of the orifice I am pointing at in the attached picture. What would cause this? Appears to me its flooding badly and that's why its not running very well. Fuel was not coming out this before, so I'm not sure what I did wrong or what needs adjusting.

 

Float height is not the same measurement as fuel height, sorry if I wasn't clear enough. ASSUMING there isn't a piece of grit or something keeping the needle and seat from closing - you did replace the needle and seat, right?

Set the float height dry i.e. no fuel, it's just a ballpark setting to get started. It may work out OK, might not. The fuel height in the bowl is a different number, and measured different, don't confuse these figures given in the manual. "Dry float height" and "Wet fuel height".

Set the float height wherever it needs to be to get the fuel height in the bowl set in spec. The 2100 on my Y block had to keep adjusting the float down where it is almost at the bottom of the carb to get the fuel height correct. The fuel height stays at 29/32" though while at idle, the float does its thing, and the needle and seat do their thing. But it's not even close to the initial "dry" float setting height.

New manufacture fuel pumps are notorious for having high pressure, that may be what's going on.

 

Got it. I cannot find the wet fuel height spec for a 400, though. I found the adjustment procedures in the manuals on Mike's website, but there is no spec. There is only a dry bowl height spec in my carb rebuild kit.


Regardless, I'm going to pull it off and reclean everything. I did replace the needle and seat.


Thanks again.

 

Hm, did see where you mentioned the fuel tank was full of sediment, so it's not unlikely maybe there's still some junk interfering with the needle seat. For fuel height level try 1" from the fuel surface to the top of the machined surface of carb, should be close enough for now.

 

I ended up replacing the tank, and ran quite a bit of gas through the lines to ensure they were clean. fuel filter has been changed, and new filter on the carb inlet. I tested fuel pressure and it was 8psi. A little on the high side, but is this enough to unseat the needle? I also disassembled and recleaned the entire carb. I could not find anything obviously dirty or wrong with the carb. I'm stumped because it starts really hard, and when it does run fuel starts to pour out those pedestal orifices which I assume is because the bowl is filling up. The float operates freely and the needle seats fine when operated manually. The fuel height in the bowl is about 1".

 

8 psi, is on the high side. 4 or 5 should be plenty. I don't know if that's enough to cause the problem though.

 

So I'm about ready to throw in the towel and just go into my build. If I get the carb for my ultimate build (750 cfm), will the truck even run with the rest stock parts?

 

I know I need to switch intake manifolds, so that would be the only non-stock part along with the carb. Will that combo run on a stock application?

 

ok........

making some assumptions that the max rpm (power band) of 5800 and assuming a VE of 90% (which is high for a street engine).....most of the 351's calc out at 530 CFM...plus 20% equals about 636 CFM......so will will a 750 single pumper work, yes, but I would highly recommend that if it's an automatic, you go with vaccume secondaries...if its a manual, vaccume will work but I would personally prefer manual secondaries.

(re- fuel psi) A little on the high side, but is this enough to unseat the needle? - No it shouldn't

But, with regards to the general issue you are having....here are my thoughts (IMHO).......

I don't care what brand carburetor you are looking at or who makes the rebuild kit......Typically the carb rebuild "kits" are crap- either missing critical parts or the parts don't fit or are of poor quality. What I have done that has worked very well for me is to go to a carb rebuilding shop and ask them to put a "kit" together for me. The cost was around $50 but every part was there, fit correctly and worked!!!!

If you need a recommendation, to get one by mail, I can suggest...

California Carburetor & Auto Repair ? Honest & Quality Repairs Done Here

CALIFORNIA CARBURETOR & AUTO REPAIR
4921 Marine Ave
Lawndale, CA 90260
(310) 679 - 1616

 

Thanks for your feedback. On the 750 cfm carb issue, I was calculating around 635 at 100% (its a 400 ci), and then upsized to 750 based on others' feedback on the site for their respective builds. My ultimate build plan is a 500+ ft/lbs goal with cam, heads, exhaust, etc. From what I read the 650 would probably work, but may be starved a bit at that hp level.


Now on the carb issue, the carb kit I bought was a "Walker" brand that I got from the local parts store. Bear with me this was before I even got on FTE and discovered Mike's carbs and the host of other great vendors and resources on this site. I don't know if this is the problem or if its something else because I have trouble replicating my problem. The truck starts immediately, and sometimes it runs fine, sometimes it starts puking fuel out the air horn overflow. When it does run fine, once it reaches operating temp it floods bad and will not restart until cold. So I'm just really frustrated and thought if I was going to spend any more money it might as well be on the new build. Plus, what's even more frustrating is my son picked up a donor truck from a relative in NE. 79 F100 with power steering, power disc breaks, and a 351m/400. It hasn't ran in who knows how long. We traced the non start back to a bad fuel pump. Replaced the fuel pump and if fired right up and runs like a champ. Never touched the carb or anything else. I know that's how it goes some times!