Triple carb install = won't start!!??

[Mike]

I think I found something. It looks like my main jets have been soldered and redrilled --

Hey Ben,

Give us a picture of your new jets as soon as they arrive. I'd like to see a comparison between the two.

[HS30-H]

Ben,

This must be one of the syptoms of Weber jets having been hard for some people to find in certain areas. I don't think there is any excuse for this kind of "make do and mend" engineering these days, as new jets are only a phone call away.

I have seen this kind of soldering and redrilling done VERY neatly in the past, but I'm afraid your jets were obviously not modified by somebody very skilled in the art!...............

Phred is dead right in stating that the carb manufacturers don't recommend that you do this. In fact, they don't even want you to "clean" the jets by poking wire into the jet orifices ( quite rightly ).

Replacing the jets with new ones will almost certainly make a huge improvement to how the engine runs.

Have you checked all the other jets and the Air Correctors too?

Good luck and let us know how you get on,

Alan T.

[EricB]

...here I am....

with the 4th of July and all and most local shops closed it was difficult to progress with my setup. I've ended up mail ordering both a fuel press guage and fuel press regulator just in case.

Just to be sure, NO ONE is using an electric pump in line with the tank somewhere at the back of the car AND AT THE SAME TIME the cam driven stock mechanical pump, right??? That would result in an overtly high fuel pressure which could "theoretically" lead to problems at the first two carbs of a three carb setup, right?

I've got the triples removed and am fitting the rubber O-rings spacers things, am putting in my header wrap and an appropriate heat shield too. I'll crawl under the back of the car today at some point and tell you just exactly which kind of electric pump is installed on the car.

-e

[Dave Sommers]

Hey ben9090, What is the finish you put on those carbs?

Very nice looking. I am redoing a set of dcoe carbs right now and want to know. Thanks

[HS30-H]

Glad you are still with us, Eric.

In answer to your query, it would certainly NOT be a good idea to run both the stock mechanical pump AND the electric pump that I presume somebody put on your car in the past. If they were plumbed so that the electric pump fed the mech. pump, then you would probably find that the mech. pump acted as a "bottle neck" and pumped only as much as it wanted up to the carbs. If they were plumbed to feed the carbs seperately then you might find that they combined at high RPM to give you slightly higher pressure than you really wanted. Best just to run the electric pump, making sure that it is wired up to run on the full voltage that it needs and only when your "accessory" switch is ON at the ignition. I guess, as its already on and been working, that this is the case.

Hooking up both a fuel pressure regulator and fuel pressure gauge will be good, and the regulator will be best sited as near to the where the fuel enters the carbs as possible. But, this will possibly lead to a dilemma with the pressure gauge, as siting it inside the engine bay will not allow you to read it when you are driving the car with the engine under varying load. You might find that you have the desired pressure at tickover and half to full throttle with the car stationary, but the pressure drops when the carbs actually get used hard on the road and the engine is under load. You need to ensure that the demand of the carbs can be met by the pressure and flow of the pump. I have seen some people site fuel pressure gauges INSIDE the passenger compartment ( obviously so that they can be read while driving the car ) but to be honest it has always seemed a little risky to me.

If you still have the return pipe connected ( back to the tank ) then this in itself will act as a kind of pressure regulator. Technically, you do not need it - as the "interruptor" design of the electric pump will only pump what is needed, and slow itself down when it is up to the desired pressure. Still, as you have seen from some of the comments before mine, some people DO still use the return pipe with an electric pump. I suppose it must make the pump work a bit harder, but as long as it can keep up it must be OK.

While those carbs are off the car and in your lap, do try to give them another once-over to check for missing parts or improper operation. Its certainly easier doing it now than when they are back on the car. Pay special attention to those "Starter Devices" as they DO need to seat properly when in the default "off" position.

If you get everything hooked up and just run the pump without cranking the engine, it should "buzz" until it gets up to pressure and then slow down to an occasional "click". You would be able to check your pressure gauge to see that the desired pressure is attained, and that the pump was not continuing to "click" fast ( meaning an obvious internal leak inside the carbs ). As mentioned before - you should get NO drips / running fuel from the carb overflows or bellmouths / trumpets with just the pump running and no actuation of the throttles / butterflies / accel. pumps. If you DO get the continual fast clicking pump and an obvious leak of fuel - then the problem is still internal in the carbs. The suspect would have to still be the float settings and their tabs that actuate the inlet of fuel.

Please remember that when you are setting the "float level" - you are actually setting the point where the inlet for the fuel opens and closes in relation to the height of the float.

Good luck again!

Alan T.

[benn9090]

Eric-

Your '73, like my '74, came from the factory with BOTH mechanical (mounted on the head) and electric fuel pumps (mounted back at the tank). The factory manual claims the electric pump's purpose is to defeat vapor lock. The manual also claims that the electric pump only operates at startup and below 750 rpm. The pressure of the two pumps is not additive. In any case, as long as the fuel pressure is reasonable (~3 psi), this should have nothing to do with your inability to start the car. In my case I have the factory electric pump still at the tank, and a "Purolator"-style electric mounted on the right front strut tower along with the regulator. I cannot yet say whether I will ultimately have fuel starvation problems or not.

Dave - My carbs are finished with Eastwood Carb Renew "Bronze", and I simply buffed the brass bits. Carb Renew is an aerosol fuel-resistant paint, essentially. You strip the carbs to bare bodies, soak in cleaner, wipe dry, plug the holes with rubber stoppers and simply spray away. One can of Carb Renew will barely do three DCOEs. You can use the leftover to touch up brake line brackets, hood prop rods, etc.

-Mark Bennett

[EricB]

just to be absolutely positively sure that my floats are set correctly now I have one more question to ask:

in the needle valve closed position, ie the top of the cylindrical floats is 7.5mm from the bottom of the carb cover, we are measuring that 7.5mm distance with the floats' tab just barely seating the needle valve in its body, right?

we are not measuring the 7.5mm position with the floats' tab fully pressing in the (check?) ball at the end of the needle valve, right?

I dissassembled them again and other than finding the starter jets (those associated with the choke or "starter devices) not being 100% clean, I did not find anything out of whack...

I am expecting the FPR and FP guage in tomorrow's delivery so I can then make sure I am getting 3psi of fuel to the triple fuel rail and no dribbling (from excess fuel pressure in the rail??) in the first two carbs.... we'll see.

-e

[HS30-H]

Eric,

I did not know that your electric pump was the type that was fitted "stock", and therefore plumbed in series with the mech. pump. You will, as Mark ( benn9090 ) quite rightly pointed out, need to make sure that it works constantly instead of just at low rpm as a back-up to the mech pump. My honest recommendation would be to remove the mech. pump when using the Webers, as it takes a lot of cranking to re-fill the fuel bowls with gas after it all evaporates. I used to find that shutting down a hot engine and then leaving the car overnight would lead to most of the fuel in the carbs actually evaporating due to heat-sink ( and making a really strong smell ). Starting up next day would require the electric pump running for a good ten seconds or so before they had refilled the carbs and got up to pressure. In fact, this has a big impact on fuel economy. I found that I was using a lot of fuel that was not getting me anywhere! Now that I do not use a triple-carb equipped Z as everyday transport I do not notice it quite so much.............

You really need to make sure that the float level measurement is taken with the tab on the float pushing on the spring-loaded ball just slightly, and with the needle just contacting its seat ( ie - closed ). That spring-loaded ball in the end of the needle valve will allow the float to keep moving higher even though the valve is closed. You need to measure the float height setting when the valve actually closes - hence my tip to blow down the pipe and hear it physically close.

Setting the other tab for the "droop" of the float is much easier, as it stops quite positively when the tab hits the outside of the needle valve body.

All the books that I have used as reference in the past seem to give different recommendations for the way to hold the carb top cover when setting the float levels. However it seems that the best way would be to stand the carb top on a flat surface on its side, at 90 degrees to the way it will be on the carb body. Don't forget that both the float parts on each carb need to measure the same - and you can't have one slightly different to the other through twisting or whatever. I guess that is fairly obvious.

When you get all your plumbing hooked up, I recommend that you take the fuel pressure reading from the carb that is furthest from the pump. That would always be the one that has the slightly lower pressure reading. Ideally you would want around 3 or 4 psi reading with the pump on and the engine not running, and a lowest reading of around 2 psi when you are running quite hard with the engine under load. Any lower than that and you have the risk of leaning out the mixture - which is not desirable ( prolonged running in this condition could lead to detonation and consequent engine damage ). Too much pressure could also overcome the needle valves and cause leaks and / or a rich mixture. These psi reading recommendations can vary, and in truth you will find that even up to 5 psi the Webers should be OK and not flood. As long as you have the 2 psi or so under load you should be OK too. I think I had around 4.5 psi stationary and 3 psi under load when we dynoed my original 40DCOE setup on the L24. Later on I had some vapour lock problems and used two pumps on the car - but nothing seemed to change adversely. Its hard to tell what the situation will be with the return feed to the tank still hooked up, but actually in your hot climate this may be of benefit to you as it will mean that the fuel is constantly circulating and not getting too hot in slow traffic.

I always found that the fuel got hottest as it passed over the transmission, rather than in the engine bay itself. I know it was certainly picking up a lot of heat from that tunnel area, so I lagged the pipe with heat-reflective wrap where it ran through there ( difficult unless the trans. is out ) and this made things a LOT better.

Fingers crossed for a good result.

Alan T.

[EricB]

Alan,

Thanks for the latest info.

Yes I did read what ben9090 said about 73s having both mech and elec pumps but in my receipts for the car (I have them dating all the way back to the original purchaser's invoice in '73) there is indeed a pamphlet on how to install an aftermarket electric pump - only problem is that the pamphlet is devoid of any branding or specs on the pump itself.... I don't discount it is possible that the '73 came with both, it just looks like that my elec is aftermarket (maybe the OEM one crapped out and this was a replacement??)

In any case before i pull the mech off I do plan on taking a fuel press reading just to get an idea what it is right now.... ie if it was indeed an excessively high FP that was making the first two dribble - that way I'll have a clear conscience on that side of things....

more news later,

-e

[benn9090]

The new main jets made a big difference to the positive! I also connected the exhaust, although in a very ugly manner, and I also took an old used 02 sensor from my '85 Supra and temporarily installed it in the front pipe and strung a voltmeter into the cockpit. Eric, you might consider doing a similar trick.

With all that done, the car runs pretty decent - only a slight stumble on progression, which according to the 02 sensor is lean - and I guess my experiience with this car and my intution say it is lean as well.

Assuming I have the 02 sensor specs correct, steady-state cruise is close to stoichiometric, just a bit to the rich side, and WOT in 3rd and 4th gear is on the rich side. I guess I could try 50 pump jets in place of my 45s to try to cure the progression stumble - any comments?

Eric- My fuel dribbling ended when I completed the exhaust connections! My theory is that reversion pulses from the crappy exhaust scavenging of an open header causes fuel to be spit back in the venturi and it creeps out between the air horn and the body. I have been told that poor synchronization will cause the same. By the way, there is a Synchrometer on EBAY for bidding for $36 (new would be about $70) ....http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=1841962591... .... and here is a good website about DCOEs http://www.cruzers.com/~twakeman/TR/WeberDCOEinfo.htm

Alan - GOOD POINT about the mechanical pump requiring a lot of time to replenish the bowls. I agree Eric should remove the mechanical pump.

Other questions:

1.) Is anyone running vac advance?

2.) PCV solutions - currently I have a breather filter on the intake (valve cover) and a long rubber pipe on the outlet (crankcase) that vents low in the engine bay back by the firewall (under the brake booster). Any other ideas?

Regards, and sorry for the long posts ....

Mark

[Doehring]

EricB,

before I forget it, when I got my 3 sk-double-carbs on my engine I had problems when driving. The car didn't accelerate smoothly but jumped like a donky. Looking at zhome.com, Index of techn. articles, Intake system I found an article "Get rid of the jerk". I did like proposed and since then the car drives fine!

Rolf

[HS30-H]

Hi Mark,

That's great news. Glad you are making some positive progress.

That stumble on progression sounds like you are a little lean on Pump Jets - so you could try that next size up, as you say. Also remember that the Idle Jets have a fairly big impact on this too; the circuits in the Webers are such that the Idle circuit overlaps with the Accel. pump stroke and you might find that richening up the mixture could help. Anyway, you are obviously really close now and you are being very proactive in hunting down the causes and cures - so you should be fine in the end.

Regarding Vacuum Advance, I ran it on my street engine and it helped a great deal with that "driveability" issue - improving the torque in low rpm range. Personally I would recommend it for a daily driver - but if the engine starts getting quite radically tuned then the matter of total advance becomes much more important and it can be blocked off. I hear lots of people debating this issue when peering inside engine bays that are triple-carb equipped. However, many of them are running worn-out and highly inaccurate old distributors that the vac. advance is not working properly on anyway! Having a distributor in tip top mechanical condition with no slop in the bearings is much more important.

Regarding venting your crankcase and cam cover - you might find that just running those pipes to the bottom of the engine bay is fine. However, you might get some oil mist in the engine bay that tends to put a fine coat of oil and crud in the engine bay, and it might be more desirable to run a race-style oil catch tank. At least if you vent the pipes low and well back you should not suffer so much from this. I eliminated any valving on mine and just ran the pipes into an aluminium catch tank mounted low on the firewall. Lots of people run those cam cover filters, so you should have no problem there.

Now lets just hope that Eric B makes good progress too.....

Alan T.