Question of power

Discussion in 'Softail Models' started by ausibatla, Dec 7, 2013.

  1. ausibatla

    ausibatla Member

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    I am still trying to work out this 1988 Springer of mine. I haven't had it long and I know it's been slightly customised with chrome aftermarket parts to make it look pretty. And everywhere I go blokes do stop and admire it. What has got me puzzeled is the engine. From the first time I rode it I knew something had been done which was why I took the compression reading. I mentioned earlier that I got 190psi but when Harley serviced it they got 200psi on each cylinder. They also said the carby wasn't standard because the 1340 evo had a 40mm Keihin. Yesterday I had to go on to reserve at 100 miles (160km) and I thought that was pretty bad considering it holds 5 U.S. gallons (19 litres). This morning I checked out the carby and it is a Mikuni flatside with an intake bore of 43.75mm.
    Firstly, can anybody tell me what I should expect before going onto reserve and what can I expect on reserve with a standard motor.
    And secondly, can anybody give me a rough guess at what may have been done to the motor to warrant a carby like this and boost compression to 200psi ?
    Cheers.
    :cheers
    :AUSTRALIA
     
  2. BUBBIE

    BUBBIE Well-Known Member

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    Probably 10.25 /10.5 to 1 compression pistons Head work ? cams? you have BUT Plenty Of Power...:D

    I can't help you as I only deal in actual miles per gallon (most USA does the same)

    Fill tank, IF you run the bike for about 80/100 miles or so, then fill again (Full tank to start with) and divide the miles by the amount of fuel (gallons) used.

    I think even your hot rod should get about 40/42 miles per gallon but IF 36 is the number it is not unusual. You really won't know what you have in that bike until you tear it down... But Why? Just enjoy the ride you are Lucky to have.

    If it is burning Clean you should be OK.

    signed....BUBBIE
     
  3. propflux01

    propflux01 Active Member

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    One other thing to check, since the bike is new to you, Are you sure its empty on petrol? I have seen petcock screen get clogged up and once it gets down a gallon or two the bike dies from fuel starvation, giving a false impression of tank being empty.
     
  4. fin_676

    fin_676 Experienced Member Staff Member Moderator Contributor

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    First thing is to check the amount of fuel in the tank the problem is that there is a small bore pipe joining the two tank half's together which will flow enough fuel to feed the carb but not enough to fill the left tank when at the pumps so I always fill left side tank first then right side and get closer to a full tank so with the tank full I would expect 150+ miles prior to reserve depending on what type of riding I am doing
    Mikuni make very good carbs for use on a Harley Davidson however the exit bore size will give the info of what it is if it uses 2 cables one to open 1 to close most likely an hsr42 if only a single cable a tm40 perhaps if the hsr42 is fitted the handlebar control has been changed to a 2 cable system

    Brian

    P.S. I just did a wee bit of checking by the early 90,s springer was fitted with a 3.5 gal tank 5 gal tank only on the custom and nostalgia
     
    Last edited: Dec 8, 2013
  5. dbmg

    dbmg Experienced Member

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    Remember fuel economy and control of right wrist go hand and hand... So if you have some performance mods done to engine to justify such a large carb,
    and bike is running like a scrared deer, then thats why your mileage is what it is....
     
  6. fin_676

    fin_676 Experienced Member Staff Member Moderator Contributor

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    The inlet bore of the carb does not directly reflect the exit bore the inlet bore of the cv 40 is 59.33mm and an exit bore of 40.38 so an inlet bore of 43.75mm is not big however mikuni inlet bore is much closer to the exit bore size I am still trying to find some mikuni dimensions

    Brian
     
  7. Jack Klarich

    Jack Klarich Expert Member

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    Popular on Evo motors were changing cams to breathe better, do you have adjustable push rods? That would be a sign of possible change to bigger and more efficient cam. Also milling heads for higher compression ratio also popular modification ( also requiring push rod change in most cases) These factors would then lead to a bigger carb and less fuel mileage, JMO
     
  8. ausibatla

    ausibatla Member

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    Thanks for those responses guys.
    It was filled to the top on both tanks and went 100 miles before reserve but once tap was turned to reserve it was O.K. so probably no blockage. It is running a little rich but would rather that than too lean. Most of my riding is done at 110kph, approximately 70mph. I live in the country and most of my runs are about 150 miles (240km) so I would like to know how far I will get on reserve. Perhaps next time I do a run I should take some fuel and run her dry. That will give me a good idea.
    Cheers.