frosty Posted July 24, 2011 Report Share Posted July 24, 2011 Do you know if any of the 4K or 5K motors have water heated inlet manifolds? I have fitted extractors onto an old 3K manifold and it needs some heat under the inlet box. I wonder if water heating the manifold would reduce a lot of the hesitation on trying to accelerate from very low revs because of speed humps, roundabouts, any other place where you have been on a trailing throttle for a while. Thoughts and ideas ? cheers Quote Link to comment Share on other sites More sharing options...
GJM85 Posted July 24, 2011 Report Share Posted July 24, 2011 (edited) negative. what size exaust are you running with the extractors? Edited July 24, 2011 by GJM85 Quote Link to comment Share on other sites More sharing options...
altezzaclub Posted July 24, 2011 Report Share Posted July 24, 2011 Brisbane!!! I thought you'd get that problem here in Orange in the snow or the -5deg frosts.... I don't think the inlet will cool enough in Brisbane to ever drop the petrol out. It sounds lean, but is there something else causing this? Are you running a stock carb and a stock cam, and a stock exhaust with the extractors? Quote Link to comment Share on other sites More sharing options...
frosty Posted July 25, 2011 Author Report Share Posted July 25, 2011 Normal system - probably about an inch 1/4 Why the questions on exhaust size?? - what effect is that going to do to the throttle response?? Quote Link to comment Share on other sites More sharing options...
xris Posted July 25, 2011 Report Share Posted July 25, 2011 back pressure. Quote Link to comment Share on other sites More sharing options...
irokin Posted July 25, 2011 Report Share Posted July 25, 2011 I don't think the inlet will cool enough in Brisbane to ever drop the petrol out. It sounds lean, but is there something else causing this? I don't think that's it. Sounds more like carby icing to me. Trailing throttle, low dewpoint, high humidity; all prime conditions for carby icing. Here's a nice graphic from the ATSB: http://www.atsb.gov.au/media/47763/carb_icing.pdf For example, on Saturday (23/7/11) at 7am, 12degC, 6degC dewpoint, 6degC dewpoint depression, 61% humidity puts you in the 'serious icing - any power' region. Later in the day, 12pm, 20degC, 5degC DP, 15degC DPD, 37% humidity; puts you in serious icing - descent power (trailing throttle ;)) Naturally the graphs a bit more aggressive than reality because its for aviation but I still think there's a fair chance its icing. Quote Link to comment Share on other sites More sharing options...
ke70dave Posted July 25, 2011 Report Share Posted July 25, 2011 aarrrggghhh that dreaded back pressure! its not back pressure! its merely a lack of scavenging effect from having an exhaust pipe that is too big. nothing to do with "pressure". and anyway this lack of scavenging effect shouldn't cause hesitation, more just a lack of low end torque. 1 Quote Link to comment Share on other sites More sharing options...
xris Posted July 25, 2011 Report Share Posted July 25, 2011 more just a lack of low end torque. sounds like a 4kc :P mine without a thermostat had a hesitation down low. with the thermostat replaced (old one had fallen to pieces) the car gets up to temp and the hesitation has disapeared. Quote Link to comment Share on other sites More sharing options...
altezzaclub Posted July 25, 2011 Report Share Posted July 25, 2011 Here's a nice graphic from the ATSB: http://www.atsb.gov..../carb_icing.pdf nice find! We're living in the dark orange zone!! Temp 7deg, dew point 2deg, humidity 90%.. a miserable day! The SUs have no heating and they run fine, although now I think about it I'm going to go right now & take off the cold air intake!! :laff: Quote Link to comment Share on other sites More sharing options...
coln72 Posted July 25, 2011 Report Share Posted July 25, 2011 My old 5k with 3KB carbies would ice up in the middle of summer on the freeway!!!!!!! Quote Link to comment Share on other sites More sharing options...
frosty Posted July 25, 2011 Author Report Share Posted July 25, 2011 Thanks Currently with mate in Melbourne Exhaust is 50mm dia from the manifold back. Standard Toyota 4K carb with 5k jetting and no pollution gear Inlet manifold is standard 3K Interesting, even in Port Macquarie, the first 15 mins or so were a cough and splutter affair until she got some revs going and some general heat in the engine bay while the top daytime temp has been about 12 or 13 degrees it is no better. :bash: Quote Link to comment Share on other sites More sharing options...
altezzaclub Posted July 26, 2011 Report Share Posted July 26, 2011 I've given my stock manifold away, but I'm sure they don't have water heating, they relied on the hotbox with the exhaust. How about a flexible intake tube to the back of the radiator, or just above the extractors to heat the air going in? Quote Link to comment Share on other sites More sharing options...
coln72 Posted July 26, 2011 Report Share Posted July 26, 2011 ^^^^^^^ That will help alot. Ran that tubing from the aircleaner down to the extractors. Didnt eliminate the issue, but made it LOTS better. Quote Link to comment Share on other sites More sharing options...
frosty Posted July 28, 2011 Author Report Share Posted July 28, 2011 Thanks heaps fellas, time to find some pipeing etc and have a bit of a play and see what comes of it. Quote Link to comment Share on other sites More sharing options...
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