Weber getting bad gas mileage

[gmask]

Well I finally decided to replace the Zenith Carbs on my 72 250 because I thought I would get better gas mileage. However currently I am getting worse gas mileage.

Can anybody give me a rundown on what to check that would greatly effect the use of gas. Clearly too much gas is being delivered as the sparkplugs are black and sooty. Perhaps I need hotter sparkplugs?

Since I had to sort of rig the accelerator linkage could that be part of the problem. Perhaps I am clueless about tuning them although they seem to be much more straight forward to tune than the Zeniths.

I need help the current gas prices in Cali are insane!!!

[gmask]

Well I found this thread

72 250 is running rich

[QUOTE]As Chuck said, Charlie is right about the transistorized system - but - it is over 30 years old. Now, my perspective (or history) with my '71 250C.

First thing I did was rebuild the Zeinth carbs, replace dizzy cap, points, rotor, plugs, plug wires, fuel pump and filters. Car ran OK but had all of the things you are talking about plus surged at highway speeds, long cold and hot starts and mileage was 10-11. Checked the coil and it was not within specs so I replaced it with a new Bosch blue coil. Car ran better - surged less at highway speeds but still not good. Replaced the Zeinth carbs with Webers and had them jetted locally by a Weber person. Much better but still not as I would have thought it to be. Mileage went to 12-13, surge at highway speeds was gone. Still rich, hesitation at start up, once in a while a backfire, rough idle now and then, hot starts still took a while, etc. Threw out the Bosch plugs and went with NGK (advice from Weber guy who just happened to be Japanese - yes we laughed about that). Made a difference. Better cold start, better idle. Still not what I wanted.

I wired the ignition around the transistor box and the hot start probem got better but overall running was off so I went back to the transistor box. Then I put the Crane XR700 and a Crane coil on and viola!! Cold start was fine, hot start (restart) problem went away, idle smoothed out, hesitation on startup was gone and the over-rich condition went away (except at idle). I opened the plug gap to .040. Mileage went to 14-15. I got 16.5 on two trips to Springfield. Weber guy told me that the rich idle with the dual Webers on my setup was just the "nature of the beast" so I never worried about it.

Now, to be totally fair here, I did scrap all of my "smog" stuff, plumbed the vacuum advance direct to the front Weber, disconnected the retard vacuum and set the initial ignition advance to 10 degrees Before. The car ran in that configuration for 5 1/2 years. Oh, the Webers did not use the fuel return so that line was capped.

My opinion is (or was) - and I could be way off base here - that the original ignition system was 30 years old and was not up to what it should have been. Plus I had to "assume" there was wear-and-tear in the dizzy also and that the Crane optical unit offset some/most/any of that wear-and-tear. I know I could have had the dizzy rebuilt but since I had no desire to maintain a totally stock MB and the thought of never having to either mess with points or ignition timing again pushed me to the Crane. For me it was a decision that I will never regret except that I should have done it when I did the Webers.

Your desires and situation may be different - but I did want you do know what I did with my 250C to solve my problems and irritations.

Good Luck.

Dan
QUOTE]

So maybe converting to a CRANE is what I need to do? I'll try some NGK's in the short run and see if that helps at all. I have a new coil and new dizzy as Dan puts it.. I guess perhaps my jets are too big as well.. who knows .. can anyone reccomend a weber guy in Los Angeles? If I can't figure this out soon I may have to put my Zeniths back in

[kilgor]

You need to dial the mixture screws in a little...

Set your idle at around 400 rpm.. it will barely run.. then set the carbs.... make them identical....

set the front one until idle increases, then back it in until it starts to die and then back out a half turn...

do the same with the back one..

then set the idle speed screws identical...

check spark plugs...

You want your vacuum at as close to 0 as possible when doing this...

[gmask]

Originally posted by kilgor
You need to dial the mixture screws in a little...
....
You want your vacuum at as close to 0 as possible when doing this...

Thanks, I will try this.. I guess having a low idle decreases the vacuum... curious... why do you need the vacuum to be low when doing this?

[kilgor]

the way a Weber works is by vacuum.. it will activate the secondary circuit and run rich if the vacuum is too high...... The secondary circuit is supposed to cut on at higher rpm----Vacuum....

I bought my kit from JAM Engineering and he told me to do it this way.. it worked out perfect...

I still need that Meter gauge to put on top to balance them and get them perfect.

[gmask]

OK well I have tuned it further.. can't tell yet if it is any better but one thing I noticed is that I do not get a nice stream of fuel when I activate the fule pump and it certainly is not consistant between the two carbs which leads me to beleive that the linkage is not installed correctly. I think I also need hotter plugs. I currently have Bosch w7dc's so I'm going to try some NGK BP5ES or BP6ES.

The other thing that bothers me is that I still have a rough idle... can't seem to get rid of it ..maybe there is a leak in the manifold but I haven't been able to find it.

[kilgor]

disconnect linkage when setting up carbs.....

the linkage that ties them together should be attached after they are tuned... They should open exactly the same...

If only one carb is squirting fuel, then one of them needs to be torn down and maybe a new diaphram....???

OR.... it may not be getting fuel???

are these new carbs?

[gmask]

Originally posted by kilgor
are these new carbs?

Yes they are fairly new (been installed for two months with little driving ) .. I'll have to check them out some more tommorrow.

Both squirt fuel but it was not in the manner I would expect.. it would certainly seem that fuel is being delivered as I am using so much of it ;-)

Another thing I noticed.. was that the sound that each carb was making was more of a gurgling percussive sound than a hissing or whine from the idle air inlet in the tops.

[DANTRCAV]

You didn't say where you got your Webers. If you got them from JAM then they will have the correct jetting for your setup. If not, then the jetting might be suspect. I got mine from a company in New York (before I heard of JAM) and they were jetted way too rich. I had them re-jetted by a local Weber expert. I think I have the jet sizes at home, if I do (and can find them) I will send the information to you.

Dan

[gmask]

Originally posted by DANTRCAV
You didn't say where you got your Webers. If you got them from JAM then they will have the correct jetting for your setup.

They are from JAM. I'm going to check the linkage again .. I had trouble making room for it.. for example the cooling hose that runs under the carbs is totally in the way and the accerator arms barely miss it. The angle that the linkage comes at the carbs seemed off when I was installing but there didn't appear to be much to do about it. I'm pretty sure I didn't overtighten the nuts on the arms.. they aren't binding there.

Your 71 250c should not have been much different than mine in this regard.. did you have any problems installing the linkage?

[gmask]

Okay the fuel squirts are better now and the air flow is really well synched between the two carbs but I still have a rough idle. I sprayed carb cleaner all over with no change until I sprayed around the top edge of the carbs. Turns out that the bolts for the carb tops were slightly loose. I tightened them and that seemed to fix things a little bit.. at least the idle does not change now when I spray around the tops... I'm quite sure that they aren't warped because the carb tops are not hot to the touch with the engine at running temp.

I'm going to put hotter sparks in this afternoon and see if that has an effect. I noticed yesterday that all but the first sparkplug was sooty.. I mean if all the sparks are not consistant that would cause a rough idle wouldn't it?

[kilgor]

clean all the plugs and redo the carbs again...

It's tedious, but it should get you a lot closer to where you need to be. IF the tops were loose.. there is no telling if it was spilling fuel constantly to foul plugs...

You might want to check your valve lash... then do the following--

Clean Plugs
Disconnect linkage
Set idle low as possible and run..
Set mixture on each..
Set idle on each the same...
re attach linkage...

see whats up!

[gmask]

I did a valve adjustment when I installed the carbs a few months ago.. I don't have time to check them again now but maybe in a few more weeks. I'm going to go ahead and try these hotter plugs just see what happens.

[gmask]

Okay more updates.. engine is running well.. the idle is still rough but not nearly as bad. I need to remember to tighten the carb tops when the engine is cold.

The car seems to like the hotter plugs. One interesting thing I noticed though is that the plug on cylinder 1 was wet with fuel and the plug on cylinder 4 was sooty.. all the others looked normal. I have a new cable set but the connector for 1 seems a bit loose

[DANTRCAV]

I did not have any trouble installing the linkage on my setup. However, I re-routed the heater hose the the fender well to get it away from the carb linkage. My linkage did lightly rub the hose when it was under the carbs. I used the stock linkage rod from the linkage arm to the carbs as it worked better than the one that came with the kit. I also replaced the stock air cleaner with two K&N's but I really doubt that had any significant affect other than they looked and sounded "cool".

Just for reference, here was the jetting on my Webers as done by the local "Weber Expert". As a side note, he also had a 250C with Webers.

Mains (Pri) 127 (Sec) 130
Air Corr (Pri) 170 (Sec) 175

Idle (S) - 50
(L) - 50

As I stated in my original post that you quoted, my setup always ran a little rich at idle but I never really had a problem with it. NGK BP5ES plugs worked the best.

Hope you get yours sorted.

Dan