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 Posted: Apr 21, 2017 03:01AM
Total posts: 8471
Last post: Aug 21, 2017
Member since:Jun 5, 2000
US
I don't remember if you have a HS or HIF series carbs.  Regardless, if you don't have a manual, visit the Burlen website for background info on how these carbs work and how to adjust them.  

Burlen Website Link

BTW, piston lifting by 1/32" (3/4mm) is the normal checking method.  If you lift that amount and the RPM drop (or the engine stalls) then the mixture is lean.

 

Doug L.
 Posted: Apr 20, 2017 06:13PM
Total posts: 101
Last post: May 4, 2017
Member since:Jan 18, 2016
Ok sorry for not replying for awhile. Carbs came off, I had enough parts to rebuild the left carb. Reassembled. Throttleshaft rebushed. Put everything on. Same thing. So unless the right carb is getting no fuel I have no idea what it is. Propane says nothing is leaking anymore. Tried switching and disabling vacuum adv, no change. Timing changes nothing. Got a pro rebuild kit coming in a few days. Guess I will try that and do both float bowls. I got brave and manually actuated the pistons whilst idling- pushing them down raises the idle. Pulling them up stalls the car. So it seems like reguardless -  More Airflow = Stalling    Less Airflow = RPMs  Its like the leaner it gets the more it revs

 Posted: Apr 17, 2017 08:20AM
Total posts: 985
Last post: Jun 25, 2017
Member since:Feb 25, 1999
Another way to check if one of the carbs is not getting fuel is to lift each dashpot (piston that the needle is attached to ) about 1/4 inch (8mm) one at a time as if you were balancing the carbs. That will stop the fuel from being drawn through the jet tube of that carb and if the engine stalls, the other carb isn't getting enough or any fuel.

'72 Morris Mini - 1310cc, K1100 head conversion

 

 

 

 Posted: Apr 17, 2017 08:00AM
Total posts: 1294
Last post: Aug 21, 2017
Member since:Oct 8, 2013
It's not the throttle shafts! It sounds to me like one carb is supplying no fuel at all. At idle the one carb can supply enough fuel to run quite nicely, the problem is when you open the throttle the none working one becomes a massive air leak because it's supplying air but no fuel. When you shut the throttle that excessive air disappears and the engine will recover and run until you open the throttle again

go back to basics check fuel supply to both carbs, check that the supply hoses are on the correct positions. Run the car at idle switch off and remove chamber tops and check level. Empty the fuel if any from the chamber check the jet pipe by blowing LOW air pressure from the jet back into the float chamber, if the carbs have sat for a while it's very possible that pipe/hose can get plugged 
 

Mini's are like buses they come along in a bunch

 Posted: Apr 17, 2017 06:55AM
Total posts: 7133
Last post: Aug 22, 2017
Member since:Feb 7, 2006
Quote:
Originally Posted by MustangMechanic1971
Do you think it's definitely a big vacuum leak? Throttle shafts are obviously leaking because the brake clean trick revs up the motor alot. I just don't see how suddenly stopping airflow makes an engine rev up so much. 
Yes for the reasons i explained above it is hard but not impossible to align the manifold correctly without the metal o rings btdt years ago when putting twins on a 998 with exactly the same issue as you are having.
A simple test is to find a piece of 1/4" or close tubing about 2 feet long and put it to you ear with the engine running check along the manifold gasket when you hear a hiss that is your leak, you can also balance the carbs this way but with worn throttle shafts they are not going to be perfect.
Joe Curto in NY sells oversize throttle shafts with the reamer to oversize the carb bodies they work excellent.
As funds are a concern you could sell the twin set up and replace it with a single HS2 1.25" or HS4 1.5" and have money in your pocket.

If in doubt, flat out . Colin Mc Rae MBE 1968-2007.

 Posted: Apr 17, 2017 03:21AM
Total posts: 3434
Last post: Aug 22, 2017
Member since:Oct 8, 2011
US
I just ran back to mention that spraying would not stop the leak but balance it's air/fuel ratio a bit. See Doug has it. Steve (CTR)

 Posted: Apr 17, 2017 03:10AM
Total posts: 8471
Last post: Aug 21, 2017
Member since:Jun 5, 2000
US
Quote:
Originally Posted by MustangMechanic1971
Do you think it's definitely a big vacuum leak? Throttle shafts are obviously leaking because the brake clean trick revs up the motor a lot. I just don't see how suddenly stopping airflow makes an engine rev up so much. 
First, do not use brake cleaner for your test.  See the article below.
http://www.brewracingframes.com/safety-alert-brake-cleaner--phosgene-gas.html

When you sprayed the cleaner at the throttle shaft it is very likely to have hit a lot of the surrounding area including the various flange gaskets.  Some people swear by using propane from an unlit torch instead of spray solvents for the test.  That can still flood the area unless the flow is low and focused. 

Your RPM results indicate that your setup has a vacuum leak.  To confirm or exclude the throttle shafts, take some thick axle grease and work it into the area where the shafts exit the carb bodies.  Yes, it will be messy but you can use that brake cleaner to wash it off later.  If your idle situation changes with the grease packed into the joints, you have found the leak.  Unfortunately the grease is only a temporary test method and won't last very long.

You also said you didn't understand how stopping the air flow affects engine speed.  The air leak isn't completely stopped by the spray solvent.  The problem is that ALL the air going into the engine needs to go through the carb throat to get mixed with the proper amount of fuel.  When additional air is allowed in either from the throttle shafts or the flange gaskets the mixture is leaned out.  It doesn't burn as well.  When you spray a flammable solvent into the path of a vacuum leak, roughly the same amount of air is being leaked in but it is being mixed with fuel which partially restores the mix AND the engine behaves like the throttle was opened up a bit to allow more fuel/air in.

Doug L.
 Posted: Apr 16, 2017 09:09PM
Total posts: 101
Last post: May 4, 2017
Member since:Jan 18, 2016
Do you think it's definitely a big vacuum leak? Throttle shafts are obviously leaking because the brake clean trick revs up the motor alot. I just don't see how suddenly stopping airflow makes an engine rev up so much. 

 Posted: Apr 16, 2017 12:47PM
Total posts: 8471
Last post: Aug 21, 2017
Member since:Jun 5, 2000
US
Quote:
Originally Posted by MustangMechanic1971
I will try cleaning & reassembling carbs and rtving gaskets some and see if that helps. 
NO.  Never, ever use RTV on anything that touches fuel.  RTV not only does not hold up against exposure to gasoline, it will sluff off threadlike bits that plug fuel systems.  

Also, no carb gaskets need sealant of any kind.  They really don't.  HS2/4/6 carbs have one gasket for the top of the float bowl.  That needs no sealant because it only needs to resist splashing gasoline.  The other gaskets go between the carb, its filter housing, and manifold spacers.  These also need no sealant.  HIF carbs also have carb/manifold gaskets but with the float bowl integrated into the carb body, they come with a square section o-ring to seal the cover to the bottom of the float chamber.  Again, no sealant on any of these gaskets.

Doug L.
 Posted: Apr 16, 2017 10:31AM
Total posts: 101
Last post: May 4, 2017
Member since:Jan 18, 2016
Yeah honestly the throttle shafts feel like they are pretty solid. The amount of play feels like none. I am wondering if I had a leak somewhere else near them. I will try cleaning & reassembling carbs and rtving gaskets some and see if that helps. 

 Posted: Apr 16, 2017 09:04AM
Total posts: 3434
Last post: Aug 22, 2017
Member since:Oct 8, 2011
US
Haven't read the whole thing but check that both carbs are getting fuel, strange things happen when both butterflys open and only one jet puts out fuel. Steve (CTR)

 Posted: Apr 16, 2017 05:51AM
Total posts: 8471
Last post: Aug 21, 2017
Member since:Jun 5, 2000
US
Check the throttle shafts by pushing and pulling them up/down, left/right... not axial movement.  If you only feel a little bit of play, leave the shafts alone for now.  Small leaks there will affect the mixture at idle and make it difficult to idle at low RPM but it won't cause the problem you are discussing.  Look for bigger air leaks between the manifold and head and the carb and the manifold.    

Once you have the big problem addressed you can determine if you need to do more to the carbs.  Oversized throttle shafts are the easiest first step.  Professional repair comes after that.  As for rebuilding, there is very little in a rebuild kit to justify its purchase without first looking at the condition of your carbs.  The kits come with a handful of gaskets that you can make at home, a jet tube that probably doesn't need replacing, and a float valve.  The float valves are probably the most important part of the kits.  So clean and inspect the carbs before spending money on parts.

Doug L.
 Posted: Apr 15, 2017 05:37PM
Total posts: 101
Last post: May 4, 2017
Member since:Jan 18, 2016
I know its overkill but I gotta make due. Am going to rebuild carbs and try sealing all gaskets up. Any cheap ways to seal up throttleshafts in the meantime?

 Posted: Apr 15, 2017 05:32PM
Total posts: 7133
Last post: Aug 22, 2017
Member since:Feb 7, 2006
You have a massive air leak. To check spray some starting fluid around the manifold gasket also check that  the dash pots have oil in them and are at the correct level. BTW throttle shaft wear is a big issue and causes higher idle problems on twin HS2's.
It is hard to align the twin HS2's manifold as they usually have metal O rings on the intake to locate on the 998/1275 head but with an 850 head you don't have that provision so they do not seal and leak air. Unless already done without some head and exhaust work twin carbs will be an overkill on an 850.

If in doubt, flat out . Colin Mc Rae MBE 1968-2007.

 Posted: Apr 15, 2017 04:19PM
Total posts: 101
Last post: May 4, 2017
Member since:Jan 18, 2016
Ok sounds weird but I had a Webber DGV on this 850 and was way too much carb. Guy gave me a manifold and 2 hs2s. Now the mini starts up and idles fine, but If I depress the accelerator nothing happens exept a small bog down on the motor. I can hold it there indefinitely and the motor runs on at about 600 rpm. As soon as I let the butterflies close, the motor revs up to that equivalent. So:
If I depress the accelerator 1/4 way, then release motor revs to maybe 2k.
1/2 ways down probably revs to like 3k as soon as I take away the butterflies. 
I can wot and motor sputters along at 600 but when I shut the throttle revs up maybe all the way to 4500. 

I am so confused! Have tried different oil combos, different mixtures, cleaned the carbs out, Tried timing, valve to rocker clearances are good. I am at a loss on these. It doesn't make sense. I have a small leak at the throttle shafts but I don't think that would cause this odd of a problem.