Hs8's

[GrahamFountain]

Sorry, stuck the picture of the HS8 throttle link up with no note by mistake. I'll write somthing tomorrow, but a bit too "refreshed" at the moment.

[gmsclassics]

This gives you an overall view of the carbs installed. Needed a narrow air filter to fit the reduced space so the trumpets could not be fitted. I renewed the engine mounts recently and now the front carb hits the bonnet at idle. I can't tell you much about the setup as the carbs came set up on a modified manifold and attached to a modified head - I haven't done anything other than install and run them as is. I can tell you that the fuel consumption is around mid 20 mpg whereas my standard car does 33 routinely. The engine with the 2" carbs is attached to an auto though. Drives well, no hestitation or hiccups so was obviously setup well at some stage. It is lumpy at idle but I suspect that is due to the cam rather than carbs. It really flies at speeds above the legal limit.

I have never really got around to sorting out the choke. It is only connected on the rear carb and often needs 'engine start' spray to fire up after a couple of days standing. There was a thread on this with some good advice:

viewtopic.php?f=4&t=19042

dolly carbs.JPG (148.31 KiB) Viewed 800 times

[dursley92]

Thanks guys, some pictures always help me to understand better. Keep them coming.

[GrahamFountain]

Here are some notes on the picture I uploded while p155ed last night. It shows the right hand side of the back carb, which is upside down, so the engine would be to the left of the pic. It probably make more sense if you copy it to a picture viewer and rotate it 180, but Like I say, I was fizzed as a part when I uploaded it, so I didn't care.

I took the throttle link plate off the manifold, to make the rest of the linkage more visible. I’m actually using a TR7 plate, which does not have the cam and follower, as in a Dolomite Sprint linkage. This is partly because I don’t know and can’t find out what this cam is for, and mostly because that was what I had. However, the procedure should be exactly the same for a dolomite throttle linkage, you just start with a different standard throttle spindle.

The set of carbs I got were complete, but while there were levers to operate the choke, they didn’t open the throttle to raise the idle speed when used and, as I rememberm they weren't linked by a choke spindle. Since I think that lifting the idle speed is an essential for cold start with a Sprint, I set too to fix this. I got the parts Burlen Fuels, but I didn’t keep the list of part numbers.

I know I had to buy the plate that goes on the left hand carb’s throttle spindle and operates the butterfly valve; the two plates that operate the chokes; the parts that the ends of the choke spindle bear in; the springs, etc., that fit these and return the choke plates; and a choke spindle.

I would have got new plate levers for both butterfly spindles, as then I'd have had two choke cam followers; but it seems that only one of the two ever existed. As I remember, the screws with the choke spindle bearings in their caps and the springs, etc., came as a kit, possible with the plate levers that operate the chokes. I also had to make a pair of spindles to goe betwix the carbs. These are exactly the same as the spindles on the standard set, but different lengths. I can see that I had to make up the throttle spindle, by cutting the standard one parallel to the lever welded on to it through the weld. I then brazed this plate onto a plain spindle rod. Since I did that, I assume that this is longer than the standard TR7 one, but I don’t remember if it’s longer than a Sprint’s: I had to do exactly the same job when making up a copy of the TR7 Sprint’s linkage. I can take these out and measure their lengths, but as it means dismounting a carb, only if that’s necessary.

On the pic, you can see the plate lever on the butterfly spindle, one of the two choke plate levers, and one end of the choke spindle and its bearing screw, etc. The two adjuster screws you can see are the idle adjuster on the left and the mixture screw on the right (as posted, upsidedown). The threaded hole in the flange on the throttle lever plate is for the choke cam follower, which I’ve still got to get. I also need the throttle return springs, but I can get those off the linkage I take out. I also need a pair of 125 thou needles, but which ones I need depends on the state of tune of the engine and how much effort the guy with the rolling road will put in, i.e. to filing down an over weak one.

The result is not quite the same as the standard HS6 set-up, because the idle is increased by only one of the choke levers. As a result it’s likely to be a bit out of balance when running on choke due to the slack in the linkage between the two carbs. As shown, the choke lever on the back carb lifts the idle speed. So I’ve got it set-up so that the choke cable goes into the front carb. Assuming the carbs are perfectly balanced for mix and idle when the choke is not being used, that should mean the front carb will be richer than the back, but the back will have the greater effect on tick over. If this isn’t right, it’s an easy job to swap the choke cable to the back carb, so it’s the richer and doing more work at idle. I say easy, but it does mean taking the screw-on nipple off the end of the choke cable and putting it back, which I always hate. Since the throttle plate is standard (either TR7 or Dolomite Sprint) the throttle cable will be standard. Any adaptation to a twin cable set-up that fits a standard set, should also fit these. The standard choke cable should also fit. The end of the cable outer will only be a few mm away from where it is on a standard set-up, but the amount of inner cable that needs to protrude might be slightly different, if the choke lever plates are different lengths from the standard ones, but I very much doubt the difference will stop a new standard one from fitting.

I’ll upload a pic of the front carb and the choke cable fittings tonight.

WRT what gmsclassics wrote (nice picture of two upturned buckets, BTW) - the front carb knocking to get out is cos the dashpot top (and damper) need shortening. I have seen one on ebay that had been modded already, but only once. Shortenting the dashpot top should be easy, with a milling machine, but I've not looked to see how to shortent the damper. I assume the plastic top puls off and you saw a bit off what's letf. If you don't do that, I suppose the carb will make its own power bulge eventually, but you might need a new plastic top for the damper first. You could take the MGC aproach (not really) - put a towel over a paving slab on the engine top and slam the lid a few times. Also you wanna watch the use of easystart spray - they get addicted.

[dursley92]

Graham, thanks for that detailed explanation. After reading it I made a start today by trying the HS8's on a manifold and then seeing if I can rob/canabalise bits off the standard set of TR7 HS6's I have. Looks like it might work but I admit I gave up because it was too cold to concentrate properly.
Re the clearance issue, I already have a dent in the bonnet of my "mule" TR7 that I have been testing the Sprint installation stuff with, but it was caused by the oil filler cap, not the carbs!

Russ

[Jon Tilson]

Sprint engine mounts can fit either way up. I think they had a cutout in them which should go uppermost. If you get it wrong the bonnet fouls slightly.

You would probably find it easier to modify the engine mounting brackets than saw the top off the carb. Just elongate the holes in the mounting bracket on the engine.

Jonners

[GrahamFountain]

I've still to actually offer the carbs up, but I'm told the HS8s fit the TR7 with no problems with the bonnet.

I got the Pipercross backplates today, and they stick a bit proud of the carb tops, so there may be a problem there. I'm pretty sure they wouldn't go under a doly's bonnet without the use of a paving slab and a lot of lid slamming. Still, since I didn't get the filters at £35 each, at worst I'm out £11.98.

So it looks like the 8s for the 7 and solexs for the doly then.