Wingsforwheels Posted October 17, 2017 Author Report Share Posted October 17, 2017 Thanks Banjo, that's what I figured. I've put caps on the ports without hoses, and plugged in the vacuum hoses to mirror the diagram on the bonnet as best I can. I've also sprayed carby cleaner in solenoid and idle screw holes, and played around with the idle mix and speed screws as Altezza suggested. It's still idling very rough or cutting out completely, and when it does idle it backfires a lot. I'm thinking now I'll take the carb out and maybe put a rebuild kit through it. I've ordered a Gregory's manual hoping that'll walk me through it, since this my first real dealings with a non-EFI car... Does that sound like a good next step before attempting to set points, timing and tappets? Quote Link to comment Share on other sites More sharing options...
altezzaclub Posted October 17, 2017 Report Share Posted October 17, 2017 Yep, do that first. Setting points and timing will alter idle speed, but by the time you do that you'll be an expert on the carb! Quote Link to comment Share on other sites More sharing options...
Banjo Posted October 17, 2017 Report Share Posted October 17, 2017 Quote I've put caps on the ports without hoses, and plugged in the vacuum hoses to mirror the diagram on the bonnet as best I can. You've got a 36 Y.O. Rolla with a Anti-Pollution tubing diagram on the inside of the bonnet, that you can still read ? This is some pristine Rolla ! Please post some pics here. If I was in Melbourne (which I'm not), I'd be around in a flash to give you a hand, & have a geek at your Rolla. Cheers Banjo. Quote Link to comment Share on other sites More sharing options...
rebuilder86 Posted October 17, 2017 Report Share Posted October 17, 2017 hey guys. Firstly be careful how u interpret altezzas mention of adjusting idle. u can so very easily be mistaken and think uve solved it when all uve done is opened the butterfly valve enough for the primary jet to engage and start dripping and it hits the butterfly valve and gets vaporized and burns. this is not ideal and is too rich. i actually bought the stock carb and it came with a bolt in the place of the solenoid for the cheap asian market to keep costs down. really don't need it here. if youd like to have it running now, u can just go to supercheap, take the solenoid with u, get a bolt with same thread from the turning stand bolts rack thing, and stick it in. or else, grind tge entire end off the solenoid and screw it in. while ur waiting for the new solenoid. no need to have a solenoid unless u get dieseling or want to invent some crazy engine management system like i did. (see my post about solenoid) Quote Link to comment Share on other sites More sharing options...
rebuilder86 Posted October 17, 2017 Report Share Posted October 17, 2017 hey guys. Firstly be careful how u interpret altezzas mention of adjusting idle. u can so very easily be mistaken and think uve solved it when all uve done is opened the butterfly valve enough for the primary jet to engage and start dripping and it hits the butterfly valve and gets vaporized and burns. this is not ideal and is too rich. i actually bought the stock carb and it came with a bolt in the place of the solenoid for the cheap asian market to keep costs down. really don't need it here. if youd like to have it running now, u can just go to supercheap, take the solenoid with u, get a bolt with same thread from the turning stand bolts rack thing, and stick it in. or else, grind tge entire end off the solenoid and screw it in. while ur waiting for the new solenoid. no need to have a solenoid unless u get dieseling or want to invent some crazy engine management system like i did. (see my post about solenoid) further. With a lean idle condition on these motors, i have found requires full manifold vacuum advance to the dizzy ao that with the advance plugged in and idle at 700, the timing should be very advanced, like over 30 degrees. if it isnt this advanced at idle this greatly lowers the power at idle and it dies. I wish i was there to help u. i have so much experience (good and bad) with this carb now, its like its part of my body. Quote Link to comment Share on other sites More sharing options...
Banjo Posted October 17, 2017 Report Share Posted October 17, 2017 (edited) Quote or else, grind the entire end off the solenoid and screw it in. while ur waiting for the new solenoid. Looking at the pic of his solenoid, that Jasper posted, when he eventually got the solenoid off, I'd say there is no need to grind it off. Looks like someone has either ground or cut the brass valve bit off altogether ! Don't forget, the idling solenoid is powered, whilst ever the engine is running. It only has one job. Its whole purpose is to stop any fuel flow, the instant you turn the ignition off, to stop engine run on. 700 rpm is a bit low for idle on these old motors ! 800-900 rpm is a better figure I have found. 30 degrees advance at idle is also a bit extreme me thinks. I think I once worked out with the centifugal bob weights in the dizzy flung right out to the stops, & with 10-12 deg of static advance, the maximum advance you can get out of a Rolla dizzy is about 34 deg. Cheers Banjo Edited October 17, 2017 by Banjo Quote Link to comment Share on other sites More sharing options...
rebuilder86 Posted October 17, 2017 Report Share Posted October 17, 2017 (edited) bugger disnt see that pic, stick it back in ans forget it. judging bybthe rust scale, id say the bowl cover (or air horn as the pros call it) needs to come off and get some elbow grease into the primary circuit, specifically the slow jet tube. banjo, ive got mine purring at 650 now haha. frikn stoked. and i didnt wanna be completely honest because whenever i bring this up people argue with me, but i have a shit idle unless the advanced idle (with vac advance plugged in) shows a timing of 35 degrees with the light. This is how i run both the 4 k motors in my life.. a 4k c in australia with points dizy with one advance tube and a dished piston 4k (4kU i think) in philippines with bosch electric 2 tube. Both run the stock flappy type carbs with only 2 vacuum ports and hot idle compensater molded into the carb shell. Perhaps its not the same for everyone else running webbers, holleys or super sized jetted stock aisans in which case the idle mix is rich enough to take care of itself at 20 degrees advance. I would be interested to see if OP can test mucking with timing and see if it gives him any joy. PLEASE NOT WITHOUT A TIMING LIGHT. I have a video on my other phone of my timing light showing the 35 degrees advance at idle and showing the timing dropping back to static as soon as load is applied and accelerator opened. it was filmed in the engine bay driving through mud just to prove a point in another forum. ill try post it here tomorow. Edited October 17, 2017 by rebuilder86 forgot stuff Quote Link to comment Share on other sites More sharing options...
Banjo Posted October 17, 2017 Report Share Posted October 17, 2017 Hi Jeremy, I think I'll just get me a Megasquirt, with adaptive mixture & idle control, that learns as it drives, & when it finds a new norm, just loads those settings to the maps. With high speed feedback control these days, with very fast micro processors, it should be possible, to constantly change all parameters, back & forth, around a base curve, to achieve the ultimate tune, which is the maximum speed possible at a combination of any load & throttle position. You can have various other "closed loop" systems working within that, but It really is that simple, when you think about it. Cheers Banjo Quote Link to comment Share on other sites More sharing options...
rebuilder86 Posted October 18, 2017 Report Share Posted October 18, 2017 cheeky bugger. megasquirt sounds like a dirty porno. does this megasquirt tech deliver spark too? (or is it all just fuel injection. anyway ive made a mistake, its 25 degrees not 35 degrees. i thought the biggeat number on the timing cover was 30 but its 20, and I'm over that at idle. Quote Link to comment Share on other sites More sharing options...
ke70dave Posted October 18, 2017 Report Share Posted October 18, 2017 Megasquirt does the lot. Fully programmable engine management system. The trick is that its so flexible that you basicallt need to build your efi and spark system from scratch. Quote Link to comment Share on other sites More sharing options...
altezzaclub Posted October 18, 2017 Report Share Posted October 18, 2017 Quote 25 degrees advance at idle and showing the timing dropping back to static as soon as load is applied and accelerator opened Yep, that's what inlet vac advance does. Then the weights opening should stick another curve on the timing as you accelerate, and when you back off at high revs you have the weight advance plus that vac advance. Out to 45-50deg advance at a guess. Then along came ported vacuum advance for the emissions control. Quote Ported vacuum sources are a result of emissions laws and manufacturers doing whatever they could to get big V8 engines to pass smog before the incorporation of the catalytic converter. The idea was that by using little to no spark advance at idle, the exhaust gas would leave the cylinder still-on-fire and help maximize the efficiency of antiquated air injection systems. Engines from this era often ran very, very hot, were prone to warped exhaust valves, cracked cylinder heads and all other manner of issues. Using a ported spark advance will still allow the vacuum advance to do its job at steady cruising, but all of the benefits of idle cooling will be lost. Not that a 4K in a dirt bin hauling up hills in 1st gear will ever need stuff that only works at highway speeds and cruise throttle! But on a road car you can set a lot of idle advance with inlet vacuum and run a leaner idle. Megasquirt one day! Quote Link to comment Share on other sites More sharing options...
rebuilder86 Posted October 18, 2017 Report Share Posted October 18, 2017 yeh I enjoy the finicky carburetor. id never trade it for EFI, not on this engine. Quote Link to comment Share on other sites More sharing options...
Wingsforwheels Posted October 18, 2017 Author Report Share Posted October 18, 2017 Quote You've got a 36 Y.O. Rolla with a Anti-Pollution tubing diagram on the inside of the bonnet, that you can still read ? This is some pristine Rolla ! Please post some pics here. Yeah she is pretty neat! Obviously some rust removal and a respray goes a long way. The last owner put these pics up on the sale ad, I'll have to take some of my own soon. Thanks for the advice guys. After half a can of carby cleaner and resetting the idle mix and speed screws, she's now idling steadily but backfiring a bit. When I spray some carb cleaner round the base of the carb the revs go up a bit, so I am thinking there is a crap gasket somewhere near there. Going to take out the carb and try to rebuild it hopefully this weekend, so fingers crossed. Quote Link to comment Share on other sites More sharing options...
rebuilder86 Posted October 19, 2017 Report Share Posted October 19, 2017 sweet jeesus its amazing. Quote Link to comment Share on other sites More sharing options...
rebuilder86 Posted October 19, 2017 Report Share Posted October 19, 2017 (edited) hey wings, if ur sure ur vacuum advance is working, a good temporary test to see if vacuum leak is still an issue after u have capped the other hoses is to remove the idle (slow) jet from inside the carb and also disable the choke from doing anything to the throttle, then see if it idles. You undo all the screws from the top of the carb, remove the pivot bolt for the accelerator pump arm, remove the top cover being carefull not to tilt it or the float assembly will fall apart, then put it aside. then u will see a little hole on the top next to the accelerator pump with a brass piece with a hole in it and a flathead screwdriver slot. undo it and use a pin on an angle to pull out the jet, its a long tube. remove it and reassemble the carb temporarily. turn choke fully off and ensure "base idle screw" is completely unwound. then turn it in until it just starts to move the throttle activator. turn the 'idle mix screw' gently all the way in and then back out only 1.5 turns. then try to start it after giving the acel pump 2 squirts. u may have to crank multiple times first to fill the fuel bowl with the mechanical pump before squirting with the accel pump. if it starts then dies, turn the 'idle mixture screw' out another half turn, if it starts and runs, let it warm up for 5 minutes then turn the mixture screw back in until it idles at something u consider reasonable and smooth. if this can be achieved, (a smooth idle with no choke) then its likely there is an internal vaccum leak at idle, (internal meaning not a hose) which greatly affects the ability of the manifold suction to pull fuel through the slow jet. the sources of internal vacuum leak are. leaking hot idle compensator rubber washer (simply plug up the hot idle compensator, u don't really need it) worn power valve piston located inside top cover, vacuum supplied from hole in the bolt through the carb(put carb in bin) leaking gasket between throttle assemblies and carby body, (rebuild kit) leaking throttle plate shafts. (put carb in the bin) the other possibilities if u get a good idle is what id reffer to as idle air bleed leaks, where unwanted air leaks in to the idle circuit and reduces the suction caused my manifold vacuum. these sourcea of leak are: the seal on the idle solenoid. (make one out of gasket paper.) the idle mix screw thread (if worn out from an obsessed user like me, grease up a new one from the rebuild kit) the top gasket where the idle air bleed hole sits over the slow jet the t slot, the transition slot itself is a source of idle air bleed during low idle. however, sometimes the t slot can be fed extra air backwards into the fuek stream if there is too much air allready in the idle circuit. a but like cappiliary action, just with airy fuel mixture. so the t slot makes it worse. nothing u can do about that but fix the air bleeding in to the slow circuit. try removing the jet, if no change, then id be looking at the float level. some people muck witg it to make it richer, then a lazy mechanic sets it back but goes to far to lean. naybe while uve got the carby cover off hang the float assembly directly vertical, carefull not to let the pivot pin fall out. if the float hangs exactly parrallel to the fasket face, its all good. Edited October 19, 2017 by rebuilder86 Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.