Danwedges Posted July 18, 2018 Report Share Posted July 18, 2018 My cars a mk3 gt6 currently running a 2000 saloon engine twin hif carbs with distributor from what I believe to be a 2500 pi engine with no vacuum advance and was wondering is there any real difference between a standard gt6 distributor to the pi distributor? The reason being is I seem to have a flat spot around 3500rpm and a lack of power after that and I'm trying to work out possible causes Any input is greatly appreciated thanks Link to comment Share on other sites More sharing options...
NonMember Posted July 18, 2018 Report Share Posted July 18, 2018 The advance curve for the PI engine is probably quite different to the 2L and probably flat from 3500 up as the PI doesn't rev. Link to comment Share on other sites More sharing options...
Nick Jones Posted July 18, 2018 Report Share Posted July 18, 2018 Which 2000 engine? There are several variations (prefix of engine no may give a clue). The later 2000 engines with domed pistons have very mild cams and don't like to rev. And this may be the fundamental problem. GT6 would have had a Delco distributor with tacho drive originally. If tacho drive not needed then stick with Lucas (slightly less crap) but the one intended for your engine code WITH vacuum advance or even invest in a 123-Tune. Nick Link to comment Share on other sites More sharing options...
Pete Lewis Posted July 18, 2018 Report Share Posted July 18, 2018 There is also club shop , H&H , Accuspark , Distirbutor doctor as alternative suppliers Of new or refurb lucas, delco , other incl tacho drives Pete Link to comment Share on other sites More sharing options...
Colin Lindsay Posted July 18, 2018 Report Share Posted July 18, 2018 4 hours ago, Nick Jones said: Which 2000 engine? There are several variations (prefix of engine no may give a clue). The later 2000 engines with domed pistons have very mild cams and don't like to rev. And this may be the fundamental problem. GT6 would have had a Delco distributor with tacho drive originally. If tacho drive not needed then stick with Lucas (slightly less crap) but the one intended for your engine code WITH vacuum advance or even invest in a 123-Tune. Nick It's funny, but I had a 123 dizzy on my GT6, and went back to the (crap?) Delco version, which was rebuilt by H&H and fitted with electronic ignition. Ebay usually lists a few, or put an ad in the Spares Wanted section if you need an original one. Link to comment Share on other sites More sharing options...
dave.vitesse Posted July 18, 2018 Report Share Posted July 18, 2018 It may not be the Dizzy. It could equally be the needles are too lean. As hif carbs weren't a standard fitment they may have needles that don't suit the 2000 engine. The vacuum advance is an economy device, it increases the ignition advance when at light throttle cruising speeds and hence improves the mixture burn efficiency.The more you use the throttle the less the vacuum unit advances the ignition as too much will cause pinking under a heaver load. It not being there shouldn't make any difference to the loss of power over 3,500 rpm. Dave Link to comment Share on other sites More sharing options...
Danwedges Posted July 18, 2018 Author Report Share Posted July 18, 2018 I'm currently running bae needles which ran my 2500 engine as I tried bcy needles and they leaned off far too much on the top end bae seems to be a good match when checking with the colour tune and the engine number is me37332he I have every intention of rebuilding my 2500 engine and replacing the 2000 when it's finished so I would like to keep the costs down and not splash out for a fancy distributor but I would like the car to pull smoothly through the revs The reason I ask is when looking on eBay at distributors some say fits 2000 /2500 so didn't know if the advance curve was different Link to comment Share on other sites More sharing options...
dave.vitesse Posted July 18, 2018 Report Share Posted July 18, 2018 Your engine is the earlier non-dome piston type. It has the 9.25:1 CR head and a Mk1 cam. BAE sound OK if you are using yellow or even green springs in the carbs. The other thing to check is that the tappets clearances are not to close. Dave Link to comment Share on other sites More sharing options...
dave.vitesse Posted July 18, 2018 Report Share Posted July 18, 2018 To answer your dizzy question. Your engine, me37332he should be fitted with a Lucas 25D6 part number 41314 dizzy. The part number is stamped on the side of the dizzy. Yes there is a difference between both early and late 2000 Mk2. Early and late 2500 PI and TC. None are the same they all have different advance curves. It will make some difference, what I am not sure. The non-vacuum type of dizzy was fitted to the TR5. Dave Link to comment Share on other sites More sharing options...
Danwedges Posted July 18, 2018 Author Report Share Posted July 18, 2018 I Have yellow and green springs I was using green on the 2500 and I've swapped back to yellow for the 2000 in attempt to solve the flat spots and lack of power to no avail. i need a suitable distributor with a tacho drive on it the engine looks to have had light headwork and it's running k&n filters Link to comment Share on other sites More sharing options...
dave.vitesse Posted July 18, 2018 Report Share Posted July 18, 2018 If the engine has a Mk1 cam still then the nearest with a tacho drive would be the Mk1 GT6 or Mk1 Vitesse dizzy. If it has a Mk2 cam then it requires a Mk2 GT6 or Mk2 Vitesse dizzy. The Vitesse Mk1 has a Lucas 22D6 part number 41168. The Mk2 Vitesse has a Lucas 22D6 part number 41273. The both Mk1 and Mk2 GT6 have a Delco type dizzy. I am not sure of their part numbers. If there are flat spots it does sound like the mixture is running too weak, maybe an air leak on the manifold? Dave Link to comment Share on other sites More sharing options...
Danwedges Posted July 18, 2018 Author Report Share Posted July 18, 2018 I assumed the same but a spray around all the joins in the manifolds with brake and parts cleaner saw no increase in revs and the colour tune shows yellow under acceleration and blue at steady revs throughout the rev range but when driving it pulls all the way up to 3500 then flat then a noticeable loss in power from 3500 onwards I had bought the engine rebuilt but never used so I have no idea of it's internal spec or cam Link to comment Share on other sites More sharing options...
Nick Jones Posted July 18, 2018 Report Share Posted July 18, 2018 Can check whether it's going lean by pulling the choke out when it goes flat - if it picks up, richer needles/heavier spring needed. @Colin - I actually hate all distributors more or less equally. There hasn't been one on my Vitesse since 2005...... 3D distributorless is the business, and a bit of rolling road time dialling in part throttle advance amply demonstrates the value of the 3rd dimension (vacuum advance in the clockwork world). Nick Link to comment Share on other sites More sharing options...
dave.vitesse Posted July 18, 2018 Report Share Posted July 18, 2018 15 minutes ago, Danwedges said: I had bought the engine rebuilt but never used so I have no idea of it's internal spec or cam If it was rebuilt as a 2000 saloon engine I would assume then it has a Mk1 cam as standard. Link to comment Share on other sites More sharing options...
thescrapman Posted July 18, 2018 Report Share Posted July 18, 2018 No vacuum advance is TR6. All thecPI I have seen have an advance. I downloaded a spreadsheet years ago that lists all spec of most Lucas dissy. Must still be out there in the ether somewhere . Link to comment Share on other sites More sharing options...
Danwedges Posted July 19, 2018 Author Report Share Posted July 19, 2018 It does seem to improve with choke above 3000 but suffers below I was under the impression that bae needles were on the rich side for the 2500 so surely they should be richer for the 2000 ? Link to comment Share on other sites More sharing options...
NonMember Posted July 19, 2018 Report Share Posted July 19, 2018 21 minutes ago, Danwedges said: I was under the impression that bae needles were on the rich side for the 2500 so surely they should be richer for the 2000 ? Why would you assume that? SU carbs are sensitive to air flow rate, not engine capacity, which is why you can largely get away with the same ones on different engines. If the engine likes a bit more fuel at high speed, the 2000 is going to get there at a lower air flow than the 2500. A 2L doing 3500RPM is flowing the same air as a 2.5L doing 2800RPM. I'm not sure that's correct but it highlights that needle selection is not a simple matter of multiplication. The people that know still seem to use trial-and-error to find the right ones. Link to comment Share on other sites More sharing options...
Danwedges Posted July 19, 2018 Author Report Share Posted July 19, 2018 When I had a similar problem with the 2500 it wouldn't rev above 3500 at all and I was suggested various needles and the bae were suggested as a rich needle that could improve performance with the cost of reduces mpg My understanding of airflow would suggest that the 2000 would require the same fuelling at 3500 revs as the 2500 requires at 2800 revs and when running the 2500 it revved freely throughout the rev range using the same needles Link to comment Share on other sites More sharing options...
Pete Lewis Posted July 19, 2018 Report Share Posted July 19, 2018 needles for SU 2000 mk2 HS4 ABU HS6 BCY my 2000 has the i hate SU HS4 and it will run its nuts off up to fever pitch despite the lax cam never set the world on fire but she gets there without a falter Pete 1 Link to comment Share on other sites More sharing options...
Nick Jones Posted July 19, 2018 Report Share Posted July 19, 2018 The dashpot springs also matter as they change the calibration range of the carb, which in turn changes which bit of the needle is in play at a particular airflow. HIF4 (rare)/HIF38 can be considered the same as HS4 in terms of needle/spring selection. Nick Link to comment Share on other sites More sharing options...
Danwedges Posted July 19, 2018 Author Report Share Posted July 19, 2018 I'm pretty sure my carbs are hif carbs have been told they could originally been dolomite sprint carbs but I'm not sure I've got a pair of bcy needles which are very lean on the top end the bae needles are defiantly an improvement on bcy Link to comment Share on other sites More sharing options...
Pete Lewis Posted July 19, 2018 Report Share Posted July 19, 2018 what is the throat/choke diameter ?? of the HIfs Link to comment Share on other sites More sharing options...
Danwedges Posted July 19, 2018 Author Report Share Posted July 19, 2018 I'm not 100% sure but I think they're 1.75" Link to comment Share on other sites More sharing options...
Pete Lewis Posted July 19, 2018 Report Share Posted July 19, 2018 so equivalent to HS6 spec. Link to comment Share on other sites More sharing options...
Danwedges Posted July 19, 2018 Author Report Share Posted July 19, 2018 I've tried bcy needles with green spring and they were leaning off too much and running to rich on idle so I returned to the bae needles I think ideally I would like to get the car on a rolling road as all of my measurements are from a gastester or gunson colourtune and they read spot on when not under load but I'm struggling to find anywhere that also stocks su needles ect to try different options Link to comment Share on other sites More sharing options...
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