Two Issues - Help (possibly related)

[Rod]

Hi All,

I have two issues that I hope I can get some direction on and I think there may be some relationship.

Firstly I am having trouble with fuel economy since doing the carby's up. I had new throttle shafts and bushes placed in my twin carby's. In addition I placed venturi restrictors corresponding with a reduction in the size of the power by-pass jet to 70. Everything else was left the same (mains were 48's). Prior to getting the carby's done up I was getting 23-23 mpg around town and up to 28-29 on a highway run. However after the alterations I was getting 16-17 around town and 19-20 on a highway run.

I then changed the jets to 47's with only marginal improvement (17-18 and 21-22). I have a set of 46's I am going to try. Has anyone run twins at less the 46. I am assuming I am not going to get the gains from 47 to 46 as expected. Any suggestions would be great. PS: Timing is spot on and carby's are in sync.

As I said the second issue may be related. I had the whole front end off last year doing repairs. On having it back on the road early in the new year I have noticed a regularly "clunk" in the front end. I have been concerned I haven't tightened things up correctly even though I believed I had. Anyway I have paid attention to it of lase and I am sure it is to do with the brakes on the front (standard breaks). It occurs after I have taken my foot off the break and it continues to roll slightly afterwards usually to a stop. I think after the "clunk" it rolls more freely. I suspect the brakes might be dragging. If this is the case what should I look for in rectifying it. I suspect if they are dragging while driving this may have a little impact on the fuel economy.

Thanks always for your impending support.

Rod

[JB]

You can see if they are dragging by feeling the temperature of the wheel after going for a drive comparing front to back... If dragging they will be hard to touch I am thinking.

[FCRB26]

Did you fit new bushes to the crossmemeber where it bolts to the subframe as they may have been ok before but after all the cleaning ect they are loose hence the front ends moving under braking and when you take your foot off the brake its rolling back .
or the out rigger bush is moving but i reckon its the subframe as the crush spacers are a set length so you cannot overtighten.
Isnt there a sequence for the spacers to go back in i remember something about it on the forum before.



Pete

[colt]

Was your car running ok before doing the carbys up? If it was I would remove the restrictors and put the jets back to where they were before. This is too big a change to be caused by a minor issue.

Stock front end? I would check the shims on the front end mounting bolts. They need to go back in the same spots.

As fevan said, check your front hubs after a drive, if you can't leave your hand on them your brakes may be dragging.

[mcl1959]

This sounds to me like a sticking wheel cylinder - Does it seem to be LH or RH side? I agree with the heat test first before pulling everything else apart.

Ken

[Harv]

G'day Rod,

The venturi restrictors sharpen up throttle response, but also apply a fair bit more suck to each of the idle, main metering and power circuits. One way to figure out which one is the culprit is to throw an exhaust gas analyser on it and see how she runs at idle, cruise and "foot buried into the floorboards" - one of them is probably running rich as buggery. If I had to guess I'd say the main metering jets, and you are heading the right way looking at the 46's.

A decent dyno mob can do the gas analysis on the rolling road, though are likely to charge a bit for the experience. The Gunson Gastester is not a bad bit of kit, and the price is comparible to two runs on the dyno... pays for itself over time if your fiddling with earlys. I've got a Gunson at home - if you're close to Sydney, you're welcome to borrow it and have a play.

Cheers,
Harv.

[zl296]

not using any more fuel....harv

just that the goverment are ripping us all off..

cheap to run an old holden....

come da revolution....

[Rod]

Thanks all for your responses. I didn't get a chance over the weekend but keen to do so soon I use this as a daily run around. Initially my first impressions were the front end Pete but took extra attention in making sure the spacers were correct following Ken's instructions at the time. I did it to the letter even using a depth gauge as highlighted in the manual. I have wondered however what happens as the new rubber blends in proper. What got me thinking it was the brakes was one day I was slightly on the downside of a hill rolling slowly when the clunk occurred. Once it did the ute rolled quicker. Ken I initially thought it was coming from front left but in recent weeks I thought it may have been the right. On the weekend I went down a dirty road and applied the breaks on and off a number of times. The brakes definitely bit more into the dirt on the front left almost locking I think.

As I said the fuel economy may be related to both issues I highlighted. Harv I forgot to mention I followed your guide to a t making sure float levels were correct, accelerator pump stroke etc... Many thanks for the offer of the Gunson but unfortunately live in Ballarat. However I have purchased a Gunson Colortune a number of years ago that I haven't used as yet. While not as good as the analyser it may give a little more insight. I have thought a little more since your post. One thing I have noticed since doing the carbys up is that I don't need to use the choke (only choke to one carby anyway) even on these current cold Ballarat mornings. I suppose this definitely narrows it down to the idle or main circuit??? Interesting though the tailpipe color seems ok. I will try the 46's and then evaluate. Harv on your investigation have you come across twins running less than 46's? (I looked at the analyser on the net-reasonably priced I thought.)

Thanks again and I will keep you posted on any success.

Rod

[GM]

Could also check the flexible brake line, they can swell and block up

[Harv]

Rod,

Have a bit of a play with it, and if you end up really, really stuck give me a yell and I'll post the analyser to you.

Not needing the choke sounds on a cold morning sounds like idle circuit, though it is possible that the extra suck is making the mains start to flow. Did you tune the idle for best vacuum? If so, it is probably idling as rich as buggery (but idles really, really well  ) - tuning the FB with both the analyser and a vacuum gauge  shows that "best vacuum idle" and "not too lean but reasonable idle" are a long way apart.

The exhaust colour is not such a great indicator of lean/rich anymore, as the absence of lead in the fuel stops the colour change you would normally see on old leaded fuel. Plugs are now a better indicator (unless of course you're running leaded avgas  ).

From the research I did, I've seen guys running as low as 44s, though every engine is different. My guess is that a lot of people who fit twins/triples ignore the loss of economy from crook tuning - there is no need to though, as multiple carbs should be just as good (and sometimes better!) if set up right.

Cheers,
Harv.

[Rod]

Thanks Harv for the generous offer. I will exhaust (excuse the pun) all other methods of elimination first. I set the idle on both carby's using the Tacho method as I didn't have access to a vacuum gauge and then finished off the sync using a Unisync. You have me thinking now. I clearly remember my frustration at the time in using the Unisync. I was able to use it great on carby but when using it on the other (front I think) it kept wanting to stall. Current me if I am wrong but this should tell me that this carby is running too rich at idle. This was funny because I was adamant that I had the idle set right based on the tacho reading.

I will try the 46's but haven't got anything lower. I got a supply from the states quite reasonable but the postage killed me and made the exercise quite expensive. If I need to get smaller ones I might put the offer out if anyone else wants a supply to share postage and handling.

Thanks Again.

Rod

PS: Glen thanks for the heads up with the brake line. At the time of putting the front end back together I thought about changing these. There arent original ones and have been changed at some point in time (15 years ago).

[Rod]

Small update. Isolated the brake at issue to the front left. Jacked old girl up and then placed foot on brake. Front right let go as you would expect while the left was locked on until I wriggled the wheel back and forth. Haven't pulled the wheel off as yet to investigate.

Changed jets in carby's (46's) and used the colortune to check at idle and part throttle. At idle I struggled to lean it off enough by the color before the motor ran rough. I then used a flat plate and slide across the throat. There was no change in engine rpm until fully blocked off. As I understand an increase in speed would have indicated a rich mixture while a drop in speed would have indicated a lean mixture. So far so good. After re-syncing I took her on a road test and she ran well. Now to wait and see if there has been any improvement in economy. By the way the plugs indicated a rich mixture but this isn't news.

I will let you you when I run a tank full through and have looked at the brakes.

Cheers

Rod

[Harv]

How did she go Rod? A little less thirsty?

Cheers,
Harv.

[Rod]

Harv,

Thanks for your interest. I have been planning to give some further figures since changing to 46's.

In a Nutshell I was getting 22-23 around town and 28-29 mpg on the open road prior to refurbishing throttle shafts and Restrictors. This was with 48 mains.

After the carby mods which included sizing down power valves I was getting 16-17 around town and 19-20 mpg on the highway. Still 48's.

The sized mains down to 47's with improvement marginal improvement to 17-18 around town and 21-22 on the road.

Since I last posted I then tried 46's. I have received the following- 19 around town, 24.7 and 23.3 on the road and 22.6 with about half around town and half on road. Still along way off what I was hoping.

I have just received a set 44's and 45's from the states (good value I thought 4 jets for $30 delivered). I am not too sure about going leaner without a dyno. It still seems to be rich at idle as I haven't had to use the choke as previously advised. Harv can you give me your run down on tuning the idle circuit (I was/are using the tacho method). I am more than confident that the two carbs are in sync / I can sync them.

I suppose where I am have some difficulties in understanding if I was getting 28 mpg on the highway with sloppy throttle shafts with 48's, surely I can lean this off more due to a richer mixture. Will investigate further and let you know. Can anyone tell me what the tell tail signs of running lean.

Thanks Again.

Rod

[Harv]

Rod,

Gotta love Strommie EE main metering jets from the States 

For the idle with a tacho:
1. Warm the car up to normal operating condition. Check the choke is off. Leave the air cleaner in place.
2. On automatics, the transmission should be in DRIVE (D) with the handbrake firmly engaged.
3. Fit the tachometer (where available).
4. Adjust both of the the slow idle adjusting screws equally until the engine idles at 480-520 rpm.
5. Adjust both the idle needle valves eqully until you get the tachometer reads maximum rpm.
6. Check the resultant engine speed, and repeat steps 4. and 5. above until a satisfactory idle is achieved (i.e. this is a circular process).
This is very similar to tuning by vacuum, in that it gives you a very rich idle. I had a play with the CO meter, and the FB is way, way rich at "maximum vacuum", and doesn't need a choke. Idles nice though  . You can lean the idles off a fair way from "max vacuum" (or "max tachometer"), but it is hard to judge just how far without exhaust gas analysis. The initial settings in the Workshop manual (idle needle valves 7/8 turn out) are a good check (note though that they apply to a single carb feeding) - if you are more than 1 turn out with twins, you are probably way rich.

Signs of leaning out (getting worse as you go down the list):
a) spark plugs get a white or very pale cream coloured deposit (not tan coloured, which is fairly normal).
b) spark plugs start to show signs of heat damage or electrode erosion.
c) vehicle begins to get a tendency to backfire (sharp cracking from the exhaust) when the lean circuit (idle, main metering or power) is operated.
d) vehicle starts to ping/detonate when lean circuit is under load. Engine runs hot.
Note that exhaust colour will barely change as you lean out due to the absence of lead in the fuel (the old trick we all learnt to tune by exhaust colour no longer applies).

Cheers,
Harv.

[newman]

G'day Rod,

I run 44's in my triple strombergs along with venturi restrictors without any drama's, my engine also runs a warm cam,headwork,extractors and electronic ignition.I also had my throttle bases rebushed before I rebuilt my strombergs and added the restrictors when I set up my triples, I tuned them with a unisync and am happy with the performance.

The strombergs are a good carburettor and I have a printed copy of Harv's "Stromberg Bible" at hand in my shed for ready reference



Mick

[Rod]

Small update for those who might be interested.

Firstly I investigated the brakes further. It was the left front. Looking at the recently bonded shoes its seemed the lining was slightly positioned to the rear of the primary shoe. You could see where was fouling on the backing plate. Took this small lip off and freed things up. However on putting it back together there was no improvement. I then backed the adjustment right off and this seemed to fix it. Adjusted up according to the manual and the drag reappeared.Mmm. I took hub / drum off again and had a partner slowly depress the brake and release it. Initially the secondary shoe didn't release hence sticking. Depressed brake slowly again and this time the same occurred with the primary. I came to the conclusion it was a sticking cylinder as Ken suggested or a compressed brake line as Brett suggested. Prior to this occurring I did clean the cylinders and renewed new cups. Put it back together and adjusted the brakes as normal and have a guess what it hasn't occurred since. Still think I will get another brake line.

As for the carby's. I used 46's for a period of time. Had two road trips and got 23.3 and 24.7 mpg and getting 20-21 mpg around town. So an improvement has been noted. However last weekend I toed a small trailer which was empty on the open road and got 17.3-18.1 mpg on two fills. So on Thursday I decided to try 45's. I tuned as normal but backed the idle adjustments right off to the point just before revs dropped. I then put the colortune in cylinder 1 and 6 (furthermost points from each carby) and the flame was what I was after. Didn't indicate a lean mixture. I have travelled about 60 miles since and I must say that the motor seems a lot smoother - may be a placebo effect. There doesn't appear to be any signs of a lean mixture. I still don't need to use the choke much either. Going by the gauge I would say there has been an improvement in economy. I will fill up tomorrow and see. I think I am not too far away from getting right setup. I have a set of 44's if I need to go further.

Cheers

Rod

[Harv]

 

Cheers,
Harv.

[FCRB26]

I remeber stuffing around with my front left hand brake set up and working out its previous owner had put the primary and secondary shoe arse about hence the grabbing drum all the time..

Sounds like your on a winner with the carbs.


Pete

[Rod]

Pete, interesting that you say that because this is the first thing I checked. I remember reading something hear about that. But no they are in the right place- primary with larger lining facing the front.

Thanks for the heads up.

Rod