5 & 6 running rich 1 - 4 OK

[Davidw]

Having read the smiles per mile thread, I just checked the mpg for my day out in the TR5 on Wednesday and it's 21.6. This coupled with the fact that the car seems to chuck out a lot of I burnt fuel led ,e to whip off the plugs. 1-4 are all a nice greyish brown while 5 is very dark grey/black and 6 is really sooty.

 

So, could it be that the two rearmost injectors are not spraying properly, or am I looking at an MU problem?

 

I have some spare KMI injectors (but they have been on the shelf for at least 12 years). Should I swap 1&2 with 5&6 first?

[Davidw]

Sorry for typo. Line 2 should read "led me..."

[ianhoward]

How long have your plugs been in? are they all of the same gap? All the same brand of plug?

 

Out of interest, I usually keep a check on mpg - something my dad always did in the past (and still does)... His reasoning is that if there is a marked change then something needs attending to - seems logical to me!

 

A good steady run on the M'way at 70mph or so and I get around 30mpg (best I have had is 32), however, B road driving and it drops to low 20's...

 

Cheers

Ian

[Davidw]

Plugs all recent (within last 1500 miles ) Gap is 35 thou but I actually had to open them up after fitting a Flamethrower coil in conjunction with the Pertronix electronic ignition. The car ran noticeably better after this adjustment back in about March with fewer misfires above 3000 rpm under load. Plugs are NGK BP6 E from Halfords.

[Nick Jones]

Throttle butterflies & linkage need synchronising. 5 & 6 are opening less thus allowing less air in but are being fuelled at the same rate as the others there mix is richer on those two.

 

Nick

[ianhoward]

David

 

I have the same plugs, Flamethrower coil and Pertronix but have the gap at 30thou - been running like this for about 6 years(?)... Haven't had any issues (that I'm aware of!)

 

Cheers

Ian

[Davidw]

I only did that about a month ago. At that time they were opening later than 1-4. I will check again on the basis that it is usually the last thing one did that causes the problem. Will report back tomorrow.

[Nick Jones]

Opening later = opening less - that's your problem I'd say.

 

Nick

[Davidw]

Definitely not the throttle levers. Checked them and they all open at exactly the same time and all to the fullest extent. I have one of Reg Bowler's overhead linkages so once set up they all turn off the same shaft - hence no loss of mechanical advantage due to wear.

 

So I changed the rearmost injectors. No 6 was quite claggy. The car started instantly and I let it get hot and I felt that there was a better quality to the exhaust i.e. much less unburnt fuel.

 

I cannot take it for a run today as my daughter has arrived with grandchildren and blocked the drive and the house is now a zoo, but I will do so tomorrow, then whip out the plugs and report back.

[Davidw]

Well the boss took all the grandchildren and daughter out so I took it for a 10 mile run. It did seem to run better and was slightly more responsive. Got home took out the plugs same old story. So this time I took off the air box, left her running and then checked the throttles. The rearmost pair (having been in synch when static) now were opening a fraction after the first 2 pairs. So I tweaked the nyloc nut on the end of the shaft and generally fiddled about until they all opened at the same time on just a touch of pedal.

 

To be sure I checked with the carburettor air flow gauge. Of course the readings at idle are all over the place with the forward throttle in each pair always reading higher. But the reading did increase on every throttle with just a touch on the pedal. As the menagerie is due back any moment, I can't take her for another run today. But I have a suspicion that this might have solved the problem.

 

I would never have thought that they throttle would behave differently when running! These cars are a constant surprise.

 

From previous posts in this subject I gather that getting the same readings from ALL throttles is a sort of Shangri La that just doesn't happen in real life, so unless someone can prove me wrong on that one, I don't think I will bother trying. Just having all cylinders burning correctly is about as much excitement as I can take! (If they are now that is)

 

Till tomorrow then.

[TR NIALL]

David,I think you will find that as things get Hotter under the Bonnet all sorts of things happen Heat Expansion being one of the biggest problems,think if you can manage to tweak Throttle Bodies and Linkage after a good run that then should be as good as it gets.

[Davidw]

Niall, that's what I did and that's what I am hoping. (Unless someone else can produce, at a reasonable cost in money and time, the post of gold at the end of the rainbow which is all throttles perfectly synchronised and all drawing exactly the same volume of air at all openings. And I suspect that the day that happens, Satan will be skating to work!)

[john.r.davies]

It may be that the OE intake plenum is a bit too narrow, With all the intakes pulling hard, and air only coming in at the front, the rears may be starved, so they run rich.

I had this and cured it by building a six inch-wide plenum, in place of the OE three inch.

Of course, if the filter is a bit clogged, that will make this effect worse, so look at that first.

 

Oh, you've cured it, well done!

John

Edited June 30, 2013 by john.r.davies

[Davidw]

No, I haven't, John. Having now established that all throttles will open simultaneously with the slightest pedal pressure, while running, I finally got to take her for a run of about 50 miles including about 35 miles of dual carriageway 75 mph cruising. Finally got the chance to whip out the plugs and same story; 1-4 greyish brown, 5 much darker, 6 black as the ace of spades. Remember I have replaced injectors 5 & 6. I sodding well give up!

 

Noting your remarks re a too narrow air intake, John, I was wondering how much damage would another 50 mile run with the air box taken off do? At least I will know that the same quantity of air must be reaching the intakes of all cylinders just before the throttles. If the rearmost two are still running rich then it must an MU fault. Maybe if I just fit a hotter plug to 5 & 6?

 

Bloody thing!

[john.r.davies]

Good test, Dave!

A damp rather than wet day, and avoiding puddles (not difficult at present!) will minimise dust and mud ingestion.

They all open at the same time, do they all open completely?

Recently, I found that a jubilee clip on a balance tube was preventing one from opening fully. I didn't note any plug changes (didn't look) but at full throttle the excess resistance in the throat could have meant rich running on those two cylinders

 

John

Edited July 2, 2013 by john.r.davies

[AndrewP]

David,

 

This issue has come up lots of times. A few folk have tried to increase plenum diameters, I fitted K&N individual filters (solved the problem, but increased induction noise) and a member has even fitted a 2nd inlet midway into the plenum to increase the air available to 5 & 6.

Not sure if any 'solve the problem' as such, but when you have 1,2,3 and 4 all pulling in air, 5 & 6 tend to get starved.

Sounds like you've confirmed a few things, but IMO, at idle the airflow shouldn't be all over the place. In fact whilst there is no magic number to look for on a flow meter, you need to ensure they are all the same, at just off idle, so around 1200-1400 rpm, and they should be steady-ish (depends on how quick to react your flow meter is I guess).

Once the throttle plate has moved about 20%, its flowing 60% of capacity (check my numbers here, it might be 80%), so you can see a small movement off the horizontal equates to a large difference in airflow. You spend more time driving around in this region than any, so its critical to get this area right.

A hotter plug at the rear as well wont hurt, as it will allow the deposits to burn off the electrode, and so prevent the plug from fouling.

Other than that, i was told that the BP ultimate/Shell uber-expensive 98 octane fuels all burn sootier (is that a word)? in engines not designed to take it. My motorbike for example is designed to run on unleaded. As soon as I put 98 ULP and unless I thrash the pants off it, tends to foul the plugs.

Perhaps try standard ULP as you may be surprised as it apparently burns cleaner in older engines (disclaimer..may be an old wives tale, but certainly makes a difference in my Kawasaki ZX7R motorbike).

Cheers

Andrew

Edited July 3, 2013 by AndrewP

[Davidw]

John & Andrew. Most grateful. I did switch to Esso 98 about three months ago as I was concerned about Ethanol in 95 grade. I also have a rear air bleed valve as well as front. This did previously help but apparently not now.

 

I will check the flow at higher throttle openings as you suggest, Andrew, and if I can get that right will take her for a run with & without the airbox & see what happens.

 

Busy for next 10 days but will report back ASAP.

[Davidw]

Right chaps. Taking Andrew's advice, tonight I warmed the car up then checked the air flow with the meter at 1500 RPM. 1-4 all were within a gnat's dangly bits but 5 & 6 were pulling less than half 1 - 4. So I know what is wrong but am unsure how to fix it. As I have one of Reg Bowler's throttle linkage kits it is not standard but it does have a threaded rod on for each pair from the shaft to the lever. Presumably, if I adjust this threaded rod to take up slack on 5 & 6, I should get an equal airflow across all 6 (at c1500 RPM)? Your thoughts would be greatly appreciated.

[john.r.davies]

Visual check - do the butterflies on 5&6 open to the same angle as the rest?

Measure the absolute opening with a pair of 'inside' calipers.

A pair of compasses would do it if you don't have the real instrument.

Are the outer edges of the disc the same distance from the inside of the throats as in the rest?

 

You should use those threaded rod adjusters to ensure that all the butterflies close at the same point.

The, if the linkage is rigid enough, then they should all open the same thoughout the range.

Do you have powerful spring pulling the throttle closed? Where is it? Does it oppose the throttle cable directly, or at one end of the linkage. Like at 5&6?

It might be twisting the link, so that they close first.

 

JOhn

Edited July 9, 2013 by john.r.davies

[Davidw]

Some excellent points, John, for which I am greatly obliged and which I will check. Likely not to be till Friday now but will report back, then.

 

Many thanks.

[Davidw]

Right chaps. First off, I am, as always, very grateful for all the help and the useful suggestions. Played hooked this afternoon and realising the antifreeze needed changing too, I put some Radflush in the coolant, fired her up and got busy with the throttle linkage. First of all, John, he only springs I have are those on the the ends of the throttle spindles so there is no uneven loading on the shaft.

 

I tried to adjust the position of 5&6 using the threaded rods and tightening the locknut on the spindle but this simply led to an idle speed of 1800 RPM. So I then put a brick on the pedal and the steering wheel bar and adjusted these until I had a steady 1800 RPM with BOTH front and rear air bleed valves fully shut. I then used the air flow meter and found that 1&2 were reading 10, 3&4 were reading 7 and 5&6 were reading 3. What I then did was to alter the relative positions of the throttle levers on the shaft (which turns when the lever attached to is is pulled by the cable as the pedal as depressed) until 1&2 and 5&6 were also reading 7(ish). Again, each pair gives different readings anyway, with the lead throttle being slightly higher.

 

As checking the openings of the throttles would have been painfully loud and rather anti-social, I then switched off and checked the openings at full throttle on the cable. The first two pairs were identically parallel to the floor of the intake tubes. 5&6 were actually over opened by about 10 degrees.

 

At idle, 5&6 are actually now more open than the first four, visually but do at least show some airflow. Between about 1500 and 2500 all pairs show almost exactly the same airflow. I suspect the throttles are all worn (yes I can wiggle them). Thus far nearly 90 minutes had passed so I took her for a blast for another hour. Back at home, while the last two plugs are slightly darker than the first four, they are at least not ally sooty.

 

But fear not for the weather, I have a clutch slip, so it'll be sunny for a good while yet!! (This will be the subject of another thread!)

 

However the thought now occurs to me that we could eliminate all this @/sing about, without going to the extreme of EFI by simply attaching an appropriately sized air flap to the airbox, after the air filter and then removing all the throttle spindles completely, plugging the spindle holes and bingo. Any thoughts on this idea?

[Davidw]

Sorry for the typos. IPad tends to autocorrect. Hope you get the gist.

[Ade_TR6]

I had a similar thought regarding this issue. The single TB would work but you need to consider the consequences of any air leaks between the TB's and the plenum. There is also the more serious issue of the plenum coming adrift and the engine effectively going WOT! May be less of a concern if you still have the original plenum support bracket in place underneath but if you have removed it, like I have, to get in an extractor manifold for instance, you may want to give it some serious thought. On a positive note there are plenty of decent sized single TB's available on eBay should you wish to have a play.

I also think that the issue of 5&6 having less air will still be a problem so you may still need to redesign the plenum with a larger volume to compensate.

 

Regards

 

Ade

 

PS agree with the iPad typing issues!!!!

[Peter Cobbold]

I had a similar thought regarding this issue. The single TB would work but you need to consider the consequences of any air leaks between the TB's and the plenum. There is also the more serious issue of the plenum coming adrift and the engine effectively going WOT! May be less of a concern if you still have the original plenum support bracket in place underneath but if you have removed it, like I have, to get in an extractor manifold for instance, you may want to give it some serious thought. On a positive note there are plenty of decent sized single TB's available on eBay should you wish to have a play.

I also think that the issue of 5&6 having less air will still be a problem so you may still need to redesign the plenum with a larger volume to compensate.

 

Regards

 

Ade

 

PS agree with the iPad typing issues!!!!

You beat me to it! If the plenum chamber slid off the manifold it would be a wild ride. And with no way other then the ig switch to kill the engine, and the steering with it ...

[Nick Jones]

I have a single throttle on the end of the plenum with my EFI setup. That makes 148 bhp from the standard PI cam and all 6 plugs are the same colour. I DOUBT the plenum size theory big-time. Just maybe on a big hp engine other wise..... no.

 

I did try the single throttle when the car was still PI equipped. It worked much better than the 6 throttles especially at idle and trickling around town, but then the original linkage was shot to bits so not a very fair comparison. At that point the original throttles were still present and tie-wrapped fully open. For some reason it also caused leaner running - to the extent that it had a marked flat-spot when opening the throttle, but the PI system was also in a pretty sad state. I do know of others who have run single throttles with great success.

 

Plenum security is vital though - as observed. Mine has 12 Jubilee clips and Tigerseal on the plenum side and I take great care that the supporting bracket is properly fitted. A solution not involving rubber tubes is on my to do list.

 

Nick